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Sample records for enhance critical current

  1. Enhancing critical current density of cuprate superconductors

    DOEpatents

    Chaudhari, Praveen

    2015-06-16

    The present invention concerns the enhancement of critical current densities in cuprate superconductors. Such enhancement of critical current densities include using wave function symmetry and restricting movement of Abrikosov (A) vortices, Josephson (J) vortices, or Abrikosov-Josephson (A-J) vortices by using the half integer vortices associated with d-wave symmetry present in the grain boundary.

  2. Enhancing superconducting critical current by randomness

    NASA Astrophysics Data System (ADS)

    Wang, Y. L.; Thoutam, L. R.; Xiao, Z. L.; Shen, B.; Pearson, J. E.; Divan, R.; Ocola, L. E.; Crabtree, G. W.; Kwok, W. K.

    2016-01-01

    The key ingredient of high critical currents in a type-II superconductor is defect sites that pin vortices. Contrary to earlier understanding on nanopatterned artificial pinning, here we show unequivocally the advantages of a random pinscape over an ordered array in a wide magnetic field range. We reveal that the better performance of a random pinscape is due to the variation of its local density of pinning sites (LDOPS), which mitigates the motion of vortices. This is confirmed by achieving even higher enhancement of the critical current through a conformally mapped random pinscape, where the distribution of the LDOPS is further enlarged. The demonstrated key role of LDOPS in enhancing superconducting critical currents gets at the heart of random versus commensurate pinning. Our findings highlight the importance of random pinscapes in enhancing the superconducting critical currents of applied superconductors.

  3. Enhancing undergraduate community placements: a critical review of current literature.

    PubMed

    Dickson, Caroline A W; Morris, Gillian; Gable, Clare

    2015-04-01

    In the face of the UK-wide policy shift to increased home care, inspiring and enabling the next generation of community nurses is more urgent than ever. The quality of the pre-registration practice learning experience is highly influential on career choices at the point of qualification. Given that 50% of learning by pre-registration students takes place in practice, mentors have a crucial role to play in preparing the next generation of nurses to work in the community. This article discusses the findings of a systematic and critical literature review of pre-registration placements that was funded by the Queen's Nursing Institute Scotland. The review found that students' experiences of learning in community settings are variable, and perceptions of students and mentors are misaligned in terms of what a quality placement should look like. Although there is no clear definition of what constitutes a community placement and there is some underuse of learning environments in areas such as general practice nursing, there are also a number of examples of new and imaginative placements. While these innovations provide 'whole experience' placements, they are currently lacking robust evaluation, despite their potential usefulness on a larger scale. Mentors have the opportunity to provide students with a range of learning opportunities that increase preparedness for working in the community, allowing final year students in particular greater influence over their learning experience. Students undertaking community practice learning, where they have a managed level of autonomy, are more likely to feel confident to take on community nursing roles. PMID:25839877

  4. Phonon-induced enhancements of the energy gap and critical current in superconducting aluminum

    SciTech Connect

    Seligson, D.

    1983-05-01

    8 to 10 GHz phonons were generated by piezoelectric transduction of a microwave and by means of a quartz delay line, were allowed to enter the aluminum only after the microwaves had long since disappeared. The maximum enhancements detected were (deltaT/T/sub c/) = -0.07, for i/sub c/ and (deltaT/T/sub c/) = -0.03 for ..delta... The power- and temperature-dependence (0.82 less than or equal to T/T/sub c/ less than or equal to 0.994) of the enhancements were compared with the prediction of a theory given by Eliashberg. The gap-enhancement was in good agreement with the theory only for low input lower. The critical current measurements are predicted to be in rough agreement with the ..delta.. measurements but this was not observed. The magnitude of the critical current enhancements was typically more than twice the observed gap enhancements. The measured critical current enhancement was relatively independent of temperature whereas the gap enhancement decreased rapidly as the temperature was lowered.

  5. Enhancement of critical current through oxygen irradiation in optimized 2G superconducting coated conductors

    NASA Astrophysics Data System (ADS)

    Kihlstrom, Karen; Leroux, M.; Welp, U.; Kwok, W.-K.; Koshelev, A. E.; Crabtree, G. W.; Rupich, M. W.; Fleshler, S.; Malozemoff, A. P.; Kayani, A.; CES Collaboration

    2015-03-01

    We demonstrate the strong enhancement of the critical current density, Jc, of commercial coated conductors (CC) in high magnetic fields using 3 MeV oxygen irradiation. The rapid suppression of Jc of coated conductors in magnetic fields remains a barrier for application of CCs in motors, generators, transformers, solenoids, and MRI systems. Using TRIM simulations, we determined that 3-MeV O-ions produce an essentially uniform defect distribution in bare CC at a rate that is ~ 2500 faster than that achieved with proton irradiation. Irradiating with 3 MeV O-ions to a dose of 1x1013 O-ions/cm2 generates a near doubling of the critical current at low temperatures: at 5K, 5T, we enhanced the critical current from 6.4 MA/cm2 to 12.2 MA/cm2. This dose can be achieved in a couple of seconds, thus this irradiation technique could be incorporated into a viable reel-to-reel production process. This work supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. D.O.E., Office of Science, Office of Basic Energy Sciences (K.K, M.L.,A.K) and by the D.O.E, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 (U.W., W.K.).

  6. Enhanced critical currents in (Gd,Y)Ba2Cu3Ox superconducting tapes with high levels of Zr addition

    NASA Astrophysics Data System (ADS)

    Selvamanickam, V.; Chen, Y.; Shi, T.; Liu, Y.; Khatri, N. D.; Liu, J.; Yao, Y.; Xiong, X.; Lei, C.; Soloveichik, S.; Galstyan, E.; Majkic, G.

    2013-03-01

    The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba2Cu3Ox film. By a modified MOCVD process, enhanced critical current densities have been achieved with high levels of Zr addition, including 3.83 MA cm-2 in 15 at.% Zr-added 1.1 μm thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/12 mm have been reached in (Gd,Y)BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape, corresponding to a pinning force value of 268 GN m-3. The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second-phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met.

  7. Enhanced critical currents in (Gd,Y)Ba2Cu3Ox superconducting tapes with high levels of Zr addition

    SciTech Connect

    Selvamanickam, V; Chen, Y; Shi, T; Liu, Y; Khatri, ND; Liu, J; Yao, Y; Xiong, X; Lei, C; Soloveichik, S; Galstyan, E; Majkic, G

    2013-01-21

    The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba2Cu3Ox film. By a modified MOCVD process,enhanced critical current densities have been achieved with high levels of Zr addition,including 3.83 MA cm(-2) in 15 at.% Zr- added 1.1 mu m thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/ 12 mm have been reached in (Gd,Y) BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape,corresponding to a pinning force value of 268 GN m(-3). The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second- phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met.

  8. Enhancement of the critical current of intrinsic Josephson junctions by carrier injection

    NASA Astrophysics Data System (ADS)

    Kizilaslan, O.; Simsek, Y.; Aksan, M. A.; Koval, Y.; Müller, P.

    2015-08-01

    We present a study of the doping effect by carrier injection of high-Tc superconducting Bi-based whiskers. The current was injected in the c-axis direction, i.e., perpendicular to the superconducting planes. Superconducting properties were investigated systematically as a function of the doping level. The doping level of one and the same sample was changed by current injection in very small steps from an underdoped state up to a slightly overdoped state. We have observed that Tc versus log (jc) exhibits a dome-shaped characteristic, which can be fitted by a parabola. As Tc versus carrier concentration has a parabolic form, too, it can be concluded that the critical current density jc increases exponentially with the doping level. The electron-trapping mechanism is interpreted in the framework of Phillips’ microscopic theory. In addition, the Joule heating effect in the intrinsic Josephson junction (IJJ) was controlled by carrier injection, and the effect of the non-equilibrium quasiparticle on the I-V curves of the IJJs was also discussed.

  9. Hydrostatic pressure: a very effective approach to significantly enhance critical current density in granular iron pnictide superconductors.

    PubMed

    Shabbir, Babar; Wang, Xiaolin; Ghorbani, S R; Shekhar, Chandra; Dou, Shixue; Srivastava, O N

    2015-01-01

    Pressure is well known to significantly raise the superconducting transition temperature, Tc, in both iron pnictides and cuprate based superconductors. Little work has been done, however, on how pressure can affect the flux pinning and critical current density in the Fe-based superconductors. Here, we propose to use hydrostatic pressure to significantly enhance flux pinning and Tc in polycrystalline pnictide bulks. We have chosen Sr4V2O6Fe2As2 polycrystalline samples as a case study. We demonstrate that the hydrostatic pressure up to 1.2 GPa can not only significantly increase Tc from 15 K (underdoped) to 22 K, but also significantly enhance the irreversibility field, Hirr, by a factor of 4 at 7 K, as well as the critical current density, Jc, by up to 30 times at both low and high fields. It was found that pressure can induce more point defects, which are mainly responsible for the Jc enhancement. Our findings provide an effective method to significantly enhance Tc, Jc, Hirr, and the upper critical field, Hc2, for other families of Fe-based superconductors in the forms of wires/tapes, films, and single crystal and polycrystalline bulks. PMID:25645351

  10. Hydrostatic pressure: A very effective approach to significantly enhance critical current density in granular iron pnictide superconductors

    PubMed Central

    Shabbir, Babar; Wang, Xiaolin; Ghorbani, S. R.; Shekhar, Chandra; Dou, Shixue; Srivastava, O. N.

    2015-01-01

    Pressure is well known to significantly raise the superconducting transition temperature, Tc, in both iron pnictides and cuprate based superconductors. Little work has been done, however, on how pressure can affect the flux pinning and critical current density in the Fe-based superconductors. Here, we propose to use hydrostatic pressure to significantly enhance flux pinning and Tc in polycrystalline pnictide bulks. We have chosen Sr4V2O6Fe2As2 polycrystalline samples as a case study. We demonstrate that the hydrostatic pressure up to 1.2 GPa can not only significantly increase Tc from 15 K (underdoped) to 22 K, but also significantly enhance the irreversibility field, Hirr, by a factor of 4 at 7 K, as well as the critical current density, Jc, by up to 30 times at both low and high fields. It was found that pressure can induce more point defects, which are mainly responsible for the Jc enhancement. Our findings provide an effective method to significantly enhance Tc, Jc, Hirr, and the upper critical field, Hc2, for other families of Fe-based superconductors in the forms of wires/tapes, films, and single crystal and polycrystalline bulks. PMID:25645351

  11. Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe.

    PubMed

    Jung, Soon-Gil; Kang, Ji-Hoon; Park, Eunsung; Lee, Sangyun; Lin, Jiunn-Yuan; Chareev, Dmitriy A; Vasiliev, Alexander N; Park, Tuson

    2015-01-01

    We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors. PMID:26548444

  12. Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe

    PubMed Central

    Jung, Soon-Gil; Kang, Ji-Hoon; Park, Eunsung; Lee, Sangyun; Lin, Jiunn-Yuan; Chareev, Dmitriy A.; Vasiliev, Alexander N.; Park, Tuson

    2015-01-01

    We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors. PMID:26548444

  13. The role of interfacial defects in enhancing the critical current density of YBa2Cu3O7-delta coatings

    SciTech Connect

    Foltyn, Stephen R; Wang, Haiyan; Civale, Leonardo; Maiorov, Boris A; Jia, Quanxi

    2009-01-01

    The critical current density (J{sub c}) of YBa{sub 2}Cu{sub 3}0{sub 7-{delta}} (YBCO) films can approach 10 MA/cm{sup 2} at 77 K in self field , but only for very thin films. We have shown previously that strong thickness dependence results if J{sub c} is enhanced near the film-substrate interface. In the present work we investigate interfacial enhancement using laser-deposited YBCO films on NdGaO{sub 3} substrates, and find that we can adjust deposition conditions to switch the enhancement on and off. Interestingly, we find that the 'on' state is accompanied by interfacial misfit dislocations, establishing an unambiguous correlation between enhanced J{sub c} and dislocations at the film-substrate interface.

  14. Enhanced critical currents of commercial 2G superconducting coated conductors through proton irradiation

    NASA Astrophysics Data System (ADS)

    Welp, Ulrich; Leroux, M.; Kihlstrom, K. J.; Kwok, W.-K.; Koshelev, A. E.; Miller, D. J.; Rupich, M. W.; Fleshler, S.; Malozemoff, A. P.; Kayani, A.

    2015-03-01

    We report on magnetization and transport measurements of the critical current density, Jc, of commercial 2G YBCO coated conductors before and after proton irradiation. The samples were irradiated along the c-axis with 4 MeV protons. Proton irradiation produces a mixed pinning landscape composed of pre-existing rare earth particles and a uniform distribution of irradiation induced nm-sized defects. This pinning landscape strongly reduces the suppression of Jc in magnetic fields resulting in a doubling of Jc in a field of ~ 4T. The irradiation dose-dependence of Jc is characterized by a temperature and field dependent sweat spot that at 5 K and 6 T occurs around 20x1016 p/cm2. Large-scale time dependent Ginzburg-Landau simulations yield a good description of our results. This work supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. D.O.E., Office of Science, Office of Basic Energy Sciences (KK, ML, AEK) and by the D.O.E, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 (UW, WKK).

  15. Enhancement of critical current density and mechanism of vortex pinning in H+-irradiated FeSe single crystal

    NASA Astrophysics Data System (ADS)

    Sun, Yue; Pyon, Sunseng; Tamegai, Tsuyoshi; Kobayashi, Ryo; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada; Kitamura, Hisashi

    2015-11-01

    We report a comprehensive study of the effect of H+ irradiation on the critical current density Jc and vortex pinning in an FeSe single crystal. The value of Jc for FeSe is enhanced by more than a factor of 2 after 3-MeV H+ irradiation, which is explained by the introduction of point pinning centers. Vortex creep rates are found to be strongly suppressed after irradiation. Detailed analyses of the pinning energy based on collective-creep-theory and an extended Maley’s method show that the H+ irradiation enhances the value of Jc before the flux creep and also reduces the size of the flux bundle, which suppresses the field dependence of Jc owing to vortex motion.

  16. Current enhancement update

    SciTech Connect

    Chambers, F.W.; Clark, J.C.; Struve, K.W.; Yu, S.S.

    1984-06-14

    Net current enhancement to levels in excess of the beam current has been observed in gases at pressures excess of 50 torr. We delineate the regimes where enhancement is observed. The experimental results fall into two very distinct classes; current enhancement at injection where the beam is only slightly displaced and current enhancement clearly associated with the high amplitude hose instability. A careful theoretical and experimental study of the diagnostics revealed no fundamental flaws although there are several complex and unlikely scenarios which could introduce fictitious current enhancement. Theoretical efforts indicate several mechanisms for generating enhancement but none of the theories can account for the detailed observations. 4 references, 4 figures.

  17. Enhanced critical currents by high-pressure impregnation of 1-2-3 systems with normal conductors

    NASA Astrophysics Data System (ADS)

    Ortabasi, Ugur; Watson, J. H.; Black, James A.

    1990-10-01

    In this paper we present the preliminary analytical and experimental results of a novel low temperature metal impregnation method to increase the critical currents in thick film and bulk HTSC materials. The method described results in a structurally more controllable and effective microcomposite than the ones obtained with metal- and metal-oxide precursors. The physical procedure involves the infiltration of the interstices of the porous, fully treated superconductor with low-melting point, low T superconductor under high pressure. Deep penetration of the metal into the granular superconducting matrix creates large surface areas of strong Proximity Effect. Improved intergrain coupling increases the DC Josephson current and therefore J, the critical current. Prior to the experimental work a theoretical study was conducted. Indium was chosen as the impregnation material. Computations showed.that the infiltrated system should have at least a four orders higher critical current (4.47 x 104 A/cm2) as compared to the same array with vacuum barriers of 20A thickness between the grains (0.31 A/cm2). On the experimental side, high T, porous, 1-2-3 samples impregnated with gallium exhibited very low contact resistance (2. 1 x 10-6 cm2) at 85°K, a value about two orders of magnitude better than the 1-2-3 systems containing intergranular silver. Further experiments with indium impregnated samples are planned. This new low temperature method allows the manufacture of highly flexible wires and films when used with suitable substrates.

  18. Enhancement of critical current of SiC and malic acid codoped MgB2/Fe wires

    NASA Astrophysics Data System (ADS)

    Li, W. X.; Chen, R. H.; Xu, X.; Hu, Y. M.; Zhu, M. Y.; Li, Y.; Dou, S. X.

    2015-09-01

    The influences of microstructure, connectivity, and disorder on the critical current density, Jc, are discussed to clarify the different mechanisms of Jc(H) in different magnetic field ranges for in situ and combined in situ/ex situ MgB2/Fe wires with nano SiC and malic acid codoping. Sintering temperature plays a very important role in the electromagnetic properties at different temperatures and under various magnetic fields. Connectivity, upper critical field, Hc2, and irreversibility field, Hirr, are studied to demonstrate the mechanism of Jc dependence on magnetic field. The combined in situ/ex situ process is proved to be a promising technique for fabrication of practical MgB2 wires.

  19. Enhancement of the critical current density in single-crystal Bi2Sr2CaCu2O8 superconductors by chemically induced disorder.

    PubMed Central

    Wang, Y L; Wu, X L; Chen, C C; Lieber, C M

    1990-01-01

    The effect of metal substitution on the critical current densities of single-crystal PbxBi2-xSr2CaCu2O8 (x = 0 or x = 0.7) superconductors has been investigated. Substitution of lead was found to increase the average critical current density from 1 x 10(5) A/cm2 to 2 x 10(6) A/cm2 at 5 K in an applied magnetic field of 10 kilooersteds (1 oersted = 80 A/m). The order of magnitude increase in the critical current density was observed for temperatures up to the flux vortex lattice melting point; the flux lattice melting point was also found to increase to 30 K (from 22 K) in the lead-substituted materials. Diffraction and microscopy investigations of the structural parameters indicate that the fundamental atomic lattices are virtually the same for both materials. Scanning tunneling microscopy images demonstrate, however, that lead substitution causes significant disorder (or defects) in the one-dimensional superstructure found in Bi2Sr2CaCu2O8. Since crystal defects can increase the critical current density by pinning the motion of flux vortices, it is likely that this lead-induced disorder enhances vortex pinning. The lead-induced disorder is specific to the nonsuperconducting Bi-O layers, and thus our results suggest that chemical substitutions may be utilized to control selectively flux pinning and the critical current density in these materials. Images PMID:11607103

  20. A study of enhancing critical current densities (J(sub c)) and critical temperature (T(sub c)) of high-temperature superconductors

    NASA Technical Reports Server (NTRS)

    Vlasse, Marcus

    1992-01-01

    The development of pure phase 123 and Bi-based 2223 superconductors has been optimized. The pre-heat processing appears to be a very important parameter in achieving optimal physical properties. The synthesis of pure phases in the Bi-based system involves effects due to oxygen partial pressure, time, and temperature. Orientation/melt-sintering effects include the extreme c-axis orientation of Yttrium 123 and Bismuth 2223, 2212, and 2201 phases. This orientation is conductive to increasing critical currents. A procedure was established to substitute Sr for Ba in Y-123 single crystals.

  1. Enhancement of low temperature Critical current density of MgB2 thin films by Au coating

    NASA Astrophysics Data System (ADS)

    Choi, Eun-Mi; Lee, Hyun-Sook; Kim, Heon-Jung; Lee, Sung-Ik; Kim, Hyeong-Jin; Kang, W. N.

    2004-03-01

    We measured the superconducting critical current densities (J_c) from the magnetization hysteresis (M-H) loop while depositing the gold on top of the MgB2 thin film. The purpose of this experiment is whether the vortex avalanche phenomena which suppress the Jc for low temperature ( T < 15 K ) and low field (H ≤ 1000 Oe) can be cured by gold deposition. This avalanche called flux noise has been headache for the application of the MgB2 thin films. As increasing the thickness of Au film, fortunately, the flux noise in the M-H loop is suppressed and finally disappears when thickness of the gold becomes 2.55 ¥im. From this experiment, the obstacles of the application of MgB2 thin film are completely overcome

  2. Enhancement at low temperatures of the critical current density for Au-coated MgB2 thin films

    NASA Astrophysics Data System (ADS)

    Choi, Eun-Mi; Lee, Hyun-Sook; Kim, Heon-Jung; Lee, Sung-Ik; Kim, Hyeong-Jin; Kang, W. N.

    2004-01-01

    We measured the superconducting critical current densities (Jc) from the magnetization hysteresis (M-H) loop for Au-coated MgB2 thin films. The purpose of this experiment was to determine whether the vortex avalanche phenomenon which suppresses the Jc for low temperature (T<15 K) and low field (H⩽1000 Oe) could be cured by gold deposition. This avalanche, called flux noise, has been a headache in applications of MgB2 thin films. Fortunately, the flux noise in the M-H loop is suppressed with increasing Au-film thickness and finally disappears when the thickness of the gold becomes 2.55 μm. We found a way to remove one obstacle for applications of MgB2 thin films as an superconducting device.

  3. High critical current superconducting tapes

    DOEpatents

    Holesinger, Terry G.; Jia, Quanxi; Foltyn, Stephen R.

    2003-09-23

    Improvements in critical current capacity for superconducting film structures are disclosed and include the use of a superconducting RE-BCO layer including a mixture of rare earth metals, e.g., yttrium and europium, where the ratio of yttrium to europium in the RE-BCO layer ranges from about 3 to 1 to from about 1.5 to 1.

  4. Method for critical current testing

    SciTech Connect

    Siddall, M.B.; Smathers, D.B.

    1989-03-01

    Superconducting critical current testing software was developed with four important features not feasible with analog test equipment. First, quasi-steady-state sample current conditions are achieved by incrementing sample current, followed by holding some milliseconds until the transient voltage decays before voltage sampling. Then the self-field correction from a helically wound sample is computed and subtracted from each sampled field reading. A copper wire inductively wound shunt which is used for quench protection has a constant measured resistance from which the shunt leakage current is computed and subtracted from the sample current by measuring the shunt voltage after each sample current reading. Finally, the critical current is recomputed from a least squares curve fit to the power law: E=A*In when the correlation coefficient for the fit is high enough to ensure a better result than the raw datum. Comparison with NBS Standard Reference Material (NbTi) and current round robin Nb/sub 3/Sn testing is examined.

  5. Enhancement of critical current density in YBa{sub 2}Cu{sub 3}O{sub 7} films using a semiconductor ion implanter

    SciTech Connect

    Matsui, H. Ootsuka, T.; Ogiso, H.; Yamasaki, H.; Sohma, M.; Yamaguchi, I.; Kumagai, T.; Manabe, T.

    2015-01-28

    An up-to-11-fold enhancement was observed in the in-magnetic-field critical current density (J{sub c}) in epitaxial YBa{sub 2}Cu{sub 3}O{sub 7} films on CeO{sub 2}-buffered SrTiO{sub 3} substrates by irradiation with 200- to 750-keV Si and 200-keV B ions. This enhancement indicates that ion beams in the range of 100 to 1000 keV, which are widely used for modifying the conductive properties of semiconducting materials, can significantly improve the vortex-pinning properties in second-generation superconducting wires. Also observed was a scaling relation between J{sub c} and the density of the vacancies (i.e., of Frenkel pairs) produced by the nuclear collisions between incident ions and target atoms, suggesting that this density is a key parameter in determining the magnitude of the J{sub c} enhancement. Also observed was an additional J{sub c} enhancement by a modification of the depth distribution of the vacancies, thus demonstrating the flexibility in controlling artificial pinning center (APC) properties in physical APC introduction.

  6. Enhancement of critical current through compound defect with proton irradiation and heavy ion irradiation in YBCO coated conductors and FeSexTe1-x crystals

    NASA Astrophysics Data System (ADS)

    Kihlstrom, Karen; Leroux, Maxime; Holleis, Sigrid; Harris, Danielle; Welp, Ulrich; Claus, Helmut; Kayani, Asghar; Gu, Genda; Rupch, Marty; Sathyamurthy, Srivatsan; Fleshler, Steven; Laviano, Francesco; Gozzelino, Laura; Gerbaldo, Roberto; Ghigo, Gianluca; Kwok, Wai-Kwong

    We investigate the enhancement of vortex pinning by both point and columnar defects and compare the results in 2G YBCO coated conductors (CC), with Tc 90K, and in FeSexTe1-x single crystals with Tc 14K. Both samples were irradiated with 250 MeV Au ions to a dose-matching field of 1T. The samples were then irradiated with 4 MeV protons to a dose of 4x1016 p/cm2 and 8x1016 p/cm2 in the CC and single crystal, respectively. The major effect of compound particle irradiation in both samples resulted in a synergetic enhancement of the critical current across a wide field range, beyond the enhancement from either individual irradiation type. This work supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. D.O.E., Office of Science, Office of Basic Energy Sciences. The work in Italy was supported by the INFN-TERASPARC project.

  7. Toward Superconducting Critical Current by Design.

    PubMed

    Sadovskyy, Ivan A; Jia, Ying; Leroux, Maxime; Kwon, Jihwan; Hu, Hefei; Fang, Lei; Chaparro, Carlos; Zhu, Shaofei; Welp, Ulrich; Zuo, Jian-Min; Zhang, Yifei; Nakasaki, Ryusuke; Selvamanickam, Venkat; Crabtree, George W; Koshelev, Alexei E; Glatz, Andreas; Kwok, Wai-Kwong

    2016-06-01

    A new critical-current-by-design paradigm is presented. It aims at predicting the optimal defect landscape in superconductors for targeted applications by elucidating the vortex dynamics responsible for the bulk critical current. To this end, critical current measurements on commercial high-temperature superconductors are combined with large-scale time-dependent Ginzburg-Landau simulations of vortex dynamics. PMID:27030115

  8. Giant enhancement in critical current density, up to a hundredfold, in superconducting NaFe0.97Co0.03 As single crystals under hydrostatic pressure.

    PubMed

    Shabbir, Babar; Wang, Xiaolin; Ghorbani, S R; Wang, A F; Dou, Shixue; Chen, X H

    2015-01-01

    Tremendous efforts towards improvement in the critical current density "Jc" of iron based superconductors (FeSCs), especially at relatively low temperatures and magnetic fields, have been made so far through different methods, resulting in real progress. Jc at high temperatures in high fields still needs to be further improved, however, in order to meet the requirements of practical applications. Here, we demonstrate a simple approach to achieve this. Hydrostatic pressure can significantly enhance Jc in NaFe0.97Co0.03As single crystals by at least tenfold at low field and more than a hundredfold at high fields. Significant enhancement in the in-field performance of NaFe0.97Co0.03As single crystal in terms of pinning force density (Fp) is found at high pressures. At high fields, the Fp is over 20 and 80 times higher than under ambient pressure at12 K and 14 K, respectively, at P = 1 GPa. We believe that the Co-doped NaFeAs compounds are very exciting and deserve to be more intensively investigated. Finally, it is worthwhile to say that by using hydrostatic pressure, we can achieve more milestones in terms of high Jc values in tapes, wires or films of other Fe-based superconductors. PMID:26030085

  9. Giant enhancement in critical current density, up to a hundredfold, in superconducting NaFe0.97Co0.03 As single crystals under hydrostatic pressure

    PubMed Central

    Shabbir, Babar; Wang, Xiaolin; Ghorbani, S. R.; Wang, A. F.; Dou, Shixue; Chen, X. H.

    2015-01-01

    Tremendous efforts towards improvement in the critical current density “Jc” of iron based superconductors (FeSCs), especially at relatively low temperatures and magnetic fields, have been made so far through different methods, resulting in real progress. Jc at high temperatures in high fields still needs to be further improved, however, in order to meet the requirements of practical applications. Here, we demonstrate a simple approach to achieve this. Hydrostatic pressure can significantly enhance Jc in NaFe0.97Co0.03As single crystals by at least tenfold at low field and more than a hundredfold at high fields. Significant enhancement in the in-field performance of NaFe0.97Co0.03As single crystal in terms of pinning force density (Fp) is found at high pressures. At high fields, the Fp is over 20 and 80 times higher than under ambient pressure at12 K and 14 K, respectively, at P = 1 GPa. We believe that the Co-doped NaFeAs compounds are very exciting and deserve to be more intensively investigated. Finally, it is worthwhile to say that by using hydrostatic pressure, we can achieve more milestones in terms of high Jc values in tapes, wires or films of other Fe-based superconductors. PMID:26030085

  10. Enhancement of the critical current density by increasing the collective pinning energy in heavy ion irradiated Co-doped BaFe2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Haberkorn, N.; Kim, Jeehoon; Gofryk, K.; Ronning, F.; Sefat, A. S.; Fang, L.; Welp, U.; Kwok, W. K.; Civale, L.

    2015-05-01

    We investigate the effect of heavy ion irradiation (1.4 GeV Pb) on the vortex matter in Ba(Fe0.92Co0.08)2As2 single crystals by superconducting quantum interference device (SQUID) magnetometry. The defects created by the irradiation are discontinuous amorphous tracks, resulting in an effective track density smaller than 25% of the nominal doses. We observe large increases in the critical current density (Jc), ranging from a factor of ∼3 at low magnetic fields to a factor of ∼10 at fields close to 1 T after irradiation with a nominal fluence of BΦ = 3.5 T. From the normalized flux creep rates (S) and the Maley analysis, we determine that the Jc increase can be mainly attributed to a large increment in the pinning energy, from <50 K to ≈500 K, while the glassy exponent μ changes from ∼1.5 to <1. Although the enhancement of Jc is substantial in the entire temperature range and S is strongly suppressed, the artificial pinning landscape induced by the irradiation does not modify significantly the crossover to fast creep in the field-temperature vortex phase diagram.

  11. Enhancement of critical current density and vortex activation energy in proton-irradiated Co-doped BaFe2As2

    NASA Astrophysics Data System (ADS)

    Taen, Toshihiro; Nakajima, Yasuyuki; Tamegai, Tsuyoshi; Kitamura, Hisashi

    2012-09-01

    The effect of proton irradiation in Ba(Fe0.93Co0.07)2As2 single crystals is reported. We analyze temperature dependence of the current density and normalized flux relaxation rate in the framework of the collective-creep model. The glassy exponent and barrier height for flux creep are directly determined by Maley's method. Our model functions for barrier height and critical current density in the absence of flux creep are explained by the superposition of δTc and δl pinnings. We also approach true critical current density by means of the generalized inversion scheme, and the obtained result is in reasonable agreement with our model function. The proton-irradiation effect on temperature dependence of the current density and normalized relaxation rate can be summarized as doubling of the barrier height at the beginning of flux creep.

  12. The Critical Current Density in High Critical Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Sengupta, Suvankar

    Critical current density, j_{ rm c}, is an important parameter for determining the usefulness. This work focuses on the understanding of various phenomena related to the j_{ rm c} in type II superconductor. Various methods to enhance j_{rm c} by introducing pinning are also considered. In particular, the effect of secondary phase addition and mechanical treatment on the microstructure and j _{rm c} of various high T _{rm c} superconducting system is investigated. Fine inclusions (<0.1 μm) can be introduced by secondary phase additions. An enhancement in j_{ rm c} is always observed associated with the presence of fine inclusions. These cavities are found to interact strongly with flux lines in a high T _{rm c} superconductor. However, the cavities are found ineffective to pin a large number of flux lines. Dislocations and other structural defects are introduced by consolidating Bi_2Sr _2CaCu_2O _{rm x} by hot isotatically pressing (HIP). Samples HIPed for 15 min. contained a high density of dislocations and showed a substantial higher j_{rm c} than the samples HIPed for 45 min. and 120 min., where most of the dislocations were annihilated during the recovery process. Various methods of determining the irreversibility line are also considered. Using the criterion of a constant j_{rm c}, the irreversibility line obtained from magnetic hysteresis measurements was found to improve with the enhancement of flux pinning and reduction of interlayer spacing. The results can be best explained by the model proposed by Kim et al (1) and Clem (2). Magnetic relaxation of various type II superconductors is also reported. The non-logarithmic of decay of magnetization can be understood by assuming a non-linear U-j relationship. A method to extract U-j relationship from magnetic relaxation experiments is also developed. The effect of flux pinning on the U-j relationship is also investigated. Melt-processed YBa_2Cu _3O_{rm x} samples with strong levitation force are also fabricated

  13. Apparatus and method for critical current measurements

    DOEpatents

    Martin, Joe A.; Dye, Robert C.

    1992-01-01

    An apparatus for the measurement of the critical current of a superconductive sample, e.g., a clad superconductive sample, the apparatus including a conductive coil, a means for maintaining the coil in proximity to a superconductive sample, an electrical connection means for passing a low amplitude alternating current through the coil, a cooling means for maintaining the superconductive sample at a preselected temperature, a means for passing a current through the superconductive sample, and, a means for monitoring reactance of the coil, is disclosed, together with a process of measuring the critical current of a superconductive material, e.g., a clad superconductive material, by placing a superconductive material into the vicinity of the conductive coil of such an apparatus, cooling the superconductive material to a preselected temperature, passing a low amplitude alternating current through the coil, the alternating current capable of generating a magnetic field sufficient to penetrate, e.g., any cladding, and to induce eddy currents in the superconductive material, passing a steadily increasing current through the superconductive material, the current characterized as having a different frequency than the alternating current, and, monitoring the reactance of the coil with a phase sensitive detector as the current passed through the superconductive material is steadily increased whereby critical current of the superconductive material can be observed as the point whereat a component of impedance deviates.

  14. Critical currents in sputtered copper molybdenum sulphide

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Woollam, J. A.; Kammerdiner, L.; Luo, H.-L.

    1977-01-01

    Critical currents in a sputtered Chevrel-phase copper molybdenum sulfide have been measured at 4.2 K as a function of applied magnetic field. Self-field critical-current values up to 10 to the 9th A/sq m were found, decreasing to 10 to the 8th A/sq m at 3 T. Graphs of pinning forces versus field were found to be independent of field direction, and the pinning mechanism is sample independent. Critical-current densities for sputtered lead molybdenum sulphide are estimated to be about 10 to the 8th A/sq m at 26 T based on a scaling law for pinning.

  15. Variable-Temperature Critical-Current Measurements

    SciTech Connect

    L. F. Goodrich; T. C. Stauffer

    2009-05-19

    This is the final report of a three year contract that covered 09/19/2005 to 07/14/2008. We requested and received a no cost time extension for the third year, 07/15/2007 to 07/14/2008, to allow DoE to send us funds if they became available during that year. It turned out that we did not receive any funding for the third year. The following paper covers our variable-temperature critical-current measurements. We made transport critical-current (Ic) measurements on commercial multifilamentary Nb3Sn strands at temperatures (T) from 4 to 17 K and magnetic fields (H) from 0 to 14 T. One of the unique features of our measurements is that we can cover a wide range of critical currents from less than 0.1 A to over 700 A.

  16. Josephson junctions with alternating critical current density

    SciTech Connect

    Mints, R.G.; Kogan, V.G.

    1997-04-01

    The magnetic-field dependence of the critical current I{sub c}(H) is considered for a short Josephson junction with the critical current density j{sub c} alternating along the tunnel contact. Two model cases, periodic and randomly alternating j{sub c}, are treated in detail. Recent experimental data on I{sub c}(H) for grain-boundary Josephson junctions in YBa{sub 2}Cu{sub 3}O{sub x} are discussed. {copyright} {ital 1997} {ital The American Physical Society}

  17. Significantly enhanced critical current density in nano-MgB2 grains rapidly formed at low temperature with homogeneous carbon doping

    NASA Astrophysics Data System (ADS)

    Liu, Yongchang; Lan, Feng; Ma, Zongqing; Chen, Ning; Li, Huijun; Barua, Shaon; Patel, Dipak; Shahriar, M.; Hossain, Al; Acar, S.; Kim, Jung Ho; Xue Dou, Shi

    2015-05-01

    High performance MgB2 bulks using carbon-coated amorphous boron as a boron precursor were fabricated by Cu-activated sintering at low temperature (600 °C, below the Mg melting point). Dense nano-MgB2 grains with a high level of homogeneous carbon doping were formed in these MgB2 samples. This type of microstructure can provide a stronger flux pinning force, together with depressed volatility and oxidation of Mg owing to the low-temperature Cu-activated sintering, leading to a significant improvement of critical current density (Jc) in the as-prepared samples. In particular, the value of Jc for the carbon-coated (Mg1.1B2)Cu0.05 sample prepared here is even above 1 × 105 A cm-2 at 20 K, 2 T. The results herein suggest that the combination of low-temperature Cu-activated sintering and employment of carbon-coated amorphous boron as a precursor could be a promising technique for the industrial production of practical MgB2 bulks or wires with excellent Jc, as the carbon-coated amorphous boron powder can be produced commercially at low cost, while the addition of Cu is very convenient and inexpensive.

  18. Architecture for high critical current superconducting tapes

    DOEpatents

    Jia, Quanxi; Foltyn, Stephen R.

    2002-01-01

    Improvements in critical current capacity for superconducting film structures are disclosed and include the use of, e.g., multilayer YBCO structures where individual YBCO layers are separated by a layer of an insulating material such as CeO.sub.2 and the like, a layer of a conducting material such as strontium ruthenium oxide and the like or by a second superconducting material such as SmBCO and the like.

  19. Enhancing Critical Thinking Skills among Authoritarian Students

    ERIC Educational Resources Information Center

    Henderson Hurley, Martha; Hurley, David

    2013-01-01

    This article focuses on assignments designed to enhance critical thinking skills for authoritarian personality types. This paper seeks to add to the literature by exploring instructional methods to overcome authoritarian traits that could inhibit the development of critical thinking skills. The article presents a strategy which can be employed…

  20. Enhancement of critical current density in a Ca0.85La0.15Fe(As0.92Sb0.08)2 superconductor with T c = 47 K through 3 MeV proton irradiation

    NASA Astrophysics Data System (ADS)

    Park, Akiyoshi; Mine, Akinori; Yamada, Tatsuhiro; Ohtake, Fumiaki; Akiyama, Hiroki; Sun, Yue; Pyon, Sunseng; Tamegai, Tsuyoshi; Kitahama, Yutaka; Mizukami, Tasuku; Kudo, Kazutaka; Nohara, Minoru; Kitamura, Hisashi

    2016-05-01

    We examine the critical current density (J c) of Ca{}1-xLa x Fe(As{}1-ySb y )2, a 112-type iron-based superconductor (IBS) with {T}{{c}} = 47 K, via magneto-optical imaging and magnetization measurements. We assert that the large self-field J c of 2.2× {10}6 A cm- 2 at 2 K is a strong indication that it is a bulk superconductor with spatially homogeneous superconductivity. A 2.8-fold enhancement in J c to 6.2× {10}6 A cm- 2 was achieved through artificially engineering pinning centers by irradiating 3 MeV protons with a total dosage of 1.0× {10}16 {{cm}}-2. The results not only demonstrate the potential of 112-type IBSs for application but also enrich the current understanding of the role of artificial defects in IBSs.

  1. Enhancement of critical currents in (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes.

    SciTech Connect

    Balachandran, U.

    1998-11-11

    The performance of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes in magnetic fields at 77 K is critical for winding this material into high-field magnets. We have recently enhanced the transport current (I{sub c}) of multifilament Ag-clad Bi-2223 tapes in a self-field at 77 K by increasing the packing density of the precursor powder improving the mechanical deformation, optimizing the conductor design, and adjusting the cooling rate. I{sub c} values of >40 A were obtained repeatedly. However, a transport current of 42 A in a self-field declined to 4 A in a 0.2 T magnetic field applied parallel to the c-axis at 77 K. A new composite tape was then fabricated in which a YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (Y-123) film was deposited on the top of the Ag-sheathed Bi-2223 tape to shield the applied magnetic field and protect the central Bi-2223 filaments. Magnetization measurements showed that the critical current densities of the Y-123-coated, Ag-sheathed Bi-2223 tapes were higher than those of an uncoated tape. These preliminary results may provide the basis for further improving the processing of long-length Bi-2223 tapes for high-field applications.

  2. Addiction: Current Criticism of the Brain Disease Paradigm

    PubMed Central

    Hammer, Rachel; Dingel, Molly; Ostergren, Jenny; Partridge, Brad; McCormick, Jennifer; Koenig, Barbara A.

    2014-01-01

    To deepen understanding of efforts to consider addiction a “brain disease,” we review critical appraisals of the disease model in conjunction with responses from in-depth semistructured stakeholder interviews with (1) patients in treatment for addiction and (2) addiction scientists. Sixty-three patients (from five alcohol and/or nicotine treatment centers in the Midwest) and 20 addiction scientists (representing genetic, molecular, behavioral, and epidemiologic research) were asked to describe their understanding of addiction, including whether they considered addiction to be a disease. To examine the NIDA brain disease paradigm, our approach includes a review of current criticism from the literature, enhanced by the voices of key stakeholders. Many argue that framing addiction as a disease will enhance therapeutic outcomes and allay moral stigma. We conclude that it is not necessary, and may be harmful, to frame addiction as a disease. PMID:24693488

  3. Critical Consciousness: Current Status and Future Directions

    ERIC Educational Resources Information Center

    Watts, Roderick J.; Diemer, Matthew A.; Voight, Adam M.

    2011-01-01

    In this chapter, the authors consider Paulo Freire's construct of critical consciousness (CC) and why it deserves more attention in research and discourse on youth political and civic development. His approach to education and similar ideas by other scholars of liberation aims to foster a critical analysis of society--and one's status within…

  4. Critical consciousness: current status and future directions.

    PubMed

    Watts, Roderick J; Diemer, Matthew A; Voight, Adam M

    2011-01-01

    In this chapter, the authors consider Paulo Freire's construct of critical consciousness (CC) and why it deserves more attention in research and discourse on youth political and civic development. His approach to education and similar ideas by other scholars of liberation aims to foster a critical analysis of society--and one's status within it--using egalitarian, empowering, and interactive methods. The aim is social change as well as learning, which makes these ideas especially relevant to the structural injustice faced by marginalized youth. From their review of these ideas, the authors derive three core CC components: critical reflection, political efficacy, and critical action. They highlight promising research related to these constructs and innovative applied work including youth action-research methodology. Their conclusion offers ideas for closing some of the critical gaps in CC theory and research. PMID:22147600

  5. Nuclear data for criticality safety - current issues

    SciTech Connect

    Leal, L.C.; Jordan, W.C.; Wright, R.Q.

    1995-06-01

    Traditionally, nuclear data evaluations have been performed in support of the analysis and design of thermal and fast reactors. In general, the neutron spectra characteristic of the thermal and fast systems used for data testing are predominantly in the low- and high-energy range with a relatively small influence from the intermediate-energy range. In the area of nuclear criticality safety, nuclear systems arising from applications involving fissionable materials outside reactors can lead to situations very different from those most commonly found in reactor analysis and design. These systems are not limited to thermal or fast and may have significant influence from the intermediate energy range. The extension of the range of applicability of the nuclear data evaluation beyond thermal and fast systems is therefore needed to cover problems found in nuclear criticality safety. Before criticality safety calculations are performed, the bias and uncertainties of the codes and cross sections that are used must be determined. The most common sources of uncertainties, in general, are the calculational methodologies and the uncertainties related to the nuclear data, such as the microscopic cross sections, entering into the calculational procedure. The aim here is to focus on the evaluated nuclear data pertaining to applications in nuclear criticality safety.

  6. Regulatory views on current criticality safety issues

    SciTech Connect

    Conde, J.M.; Recio, M.

    1996-12-31

    The nuclear facilities in Spain of interest from the stand-point of criticality are a fuel fabrication facility, handling only fresh fuel; seven pressurized water reactor (PWR) plants with different nuclear steam supply system designs; two boiling water reactor (BWR) plants; and an ongoing program of dual-purpose casks (storage and transport) for spent fuel. Given the spent-fuel storage space problems with the original rack designs, a plan was developed and started in 1990 to incorporate high-density racks (borated steel or Boral) in the spent-fuel storage of all plants, giving credit for fuel burnup. Following this plan, five PWR units have licensed burnup-credited criticality safety analyses using a two-zone approach (fresh and spent fuel) for the spent-fuel pool. The two BWR plants have also licensed a criticality safety analysis with credit for the reactivity reduction provided by the gadolinia rods. The only spent-fuel cask yet licensed has followed the expected fresh fuel assumption for the criticality safety evaluation. However, it can be expected that the industry will submit burnup-credit safety analyses for the future casks designs.

  7. High-field critical current enhancement by irradiation induced correlated and random defects in (Ba{sub 0.6}K{sub 0.4})Fe{sub 2}As{sub 2}

    SciTech Connect

    Kihlstrom, K. J.; Crabtree, G. W.; Fang, L.; Jia, Y.; Shen, B.; Koshelev, A. E.; Welp, U.; Kwok, W.-K.; Kayani, A.; Zhu, S. F.; Wen, H.-H.

    2013-11-11

    Mixed pinning landscapes in superconductors are emerging as an effective strategy to achieve high critical currents in high, applied magnetic fields. Here, we use heavy-ion and proton irradiation to create correlated and point defects to explore the vortex pinning behavior of each and combined constituent defects in the iron-based superconductor Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2} and find that the pinning mechanisms are non-additive. The major effect of p-irradiation in mixed pinning landscapes is the generation of field-independent critical currents in very high fields. At 7 T ‖ c and 5 K, the critical current density exceeds 5 MA/cm{sup 2}.

  8. Numerical optimization methods for critical currents in superconductors

    NASA Astrophysics Data System (ADS)

    Kimmel, Gregory; Sadovskyy, Ivan; Koshelev, Alex; Glatz, Andreas

    In this work, I present optimization methods for maximizing the critical current in high-temperature superconductors for energy applications. The critical current in the presence of an external magnetic field is mostly defined by the pinning landscape (pinscape) within the superconductor, which prevents magnetic vortices from moving and, therefore, increases its critical current. Our approach is to generate different pinscapes and obtain the resulting critical current by large-scale time-dependent Ginzburg-Landau equations. Pinning centers could be any combination of defects, including spherical and columnar defects. The parameters controlling the pinscape are adaptively adjusted in order to find the optimal parameter set, which maximizes the critical current. Here, we compare different optimization methods and discuss their performance. Work was supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences.

  9. Use of a Web Site to Enhance Criticality Safety Training

    SciTech Connect

    Huang, S T; Morman, J

    2003-08-04

    Currently, a website dedicated to enhancing communication and dissemination of criticality safety information is sponsored by the U.S. Department of Energy (DOE) Nuclear Criticality Safety Program (NCSP). This website was developed as part of the DOE response to the Defense Nuclear Facilities Safety Board (DNFSB) Recommendation 97-2, which reflected the need to make criticality safety information available to a wide audience. The website is the focal point for DOE nuclear criticality safety (NCS) activities, resources and references, including hyperlinks to other sites actively involved in the collection and dissemination of criticality safety information. The website is maintained by the Lawrence Livermore National Laboratory (LLNL) under auspices of the NCSP management. One area of the website contains a series of Nuclear Criticality Safety Engineer Training (NCSET) modules. During the past few years, many users worldwide have accessed the NCSET section of the NCSP website and have downloaded the training modules as an aid for their training programs. This trend was remarkable in that it points out a continuing need of the criticality safety community across the globe. It has long been recognized that training of criticality safety professionals is a continuing process involving both knowledge-based training and experience-based operations floor training. As more of the experienced criticality safety professionals reach retirement age, the opportunities for mentoring programs are reduced. It is essential that some method be provided to assist the training of young criticality safety professionals to replenish this limited human expert resource to support on-going and future nuclear operations. The main objective of this paper is to present the features of the NCSP website, including its mission, contents, and most importantly its use for the dissemination of training modules to the criticality safety community. We will discuss lessons learned and several ideas

  10. Enhancing Critical Thinking with Aesthetic, Critical, and Creative Inquiry

    ERIC Educational Resources Information Center

    Lampert, Nancy

    2006-01-01

    Inquiry-based classroom activities require students to solve problems and answer questions that have more than one possible resolution. These types of activities stimulate critical thinking skills and dispositions in students. PreK-12 art classrooms are rich with opportunity for inquiry-based activities for children and adolescents. This article…

  11. Critical current versus strain research at the University of Twente

    NASA Astrophysics Data System (ADS)

    van Eck, H. J. N.; van der Laan, D. C.; Dhallé, M.; ten Haken, B.; ten Kate, H. H. J.

    2003-09-01

    At the University of Twente a U-shaped spring has been used to investigate the mechanical properties of a large variety of superconducting tapes and wires. Several mechanisms are responsible for the degradation of critical current as a function of applied strain. A change in its intrinsic parameters causes a reversible critical current dependence in Nb3Sn. The critical current reaches a maximum at a wire-dependent tensile strain level, and decreases when this tensile strain is either released or further increased. In Bi-based tapes the critical current is virtually insensitive to tensile strain up to a sample-dependent irreversible strain limit. When this limit is exceeded, the critical current decreases steeply and irreversibly. This behaviour is attributed to microstructural damage to the filaments. This cracking of the filaments is verified by a magneto-optical strain experiment. Recent experiments suggest that in MgB2 the degradation of critical current is caused by a change in intrinsic properties and damage to the microstructure. Magneto-optical imaging can be used to investigate the influence of applied strain on the microstructure of MgB2, as is done successfully with Bi-based tapes. In all these conductors the thermal precompression of the filaments plays an important role. In Nb3Sn it determines the position of the maximum and in Bi-based and MgB2 conductors it is closely related to the irreversible strain limit.

  12. Non Pharmacological Cognitive Enhancers - Current Perspectives.

    PubMed

    Sachdeva, Ankur; Kumar, Kuldip; Anand, Kuljeet Singh

    2015-07-01

    Cognition refers to the mental processes involved in thinking, knowing, remembering, judging, and problem solving. Cognitive dysfunctions are an integral part of neuropsychiatric disorders as well as in healthy ageing. Cognitive Enhancers are molecules that help improve aspects of cognition like memory, intelligence, motivation, attention and concentration. Recently, Non Pharmacological Cognitive Enhancers have gained popularity as effective and safe alternative to various established drugs. Many of these Non Pharmacological Cognitive Enhancers seem to be more efficacious compared to currently available Pharmacological Cognitive Enhancers. This review describes and summarizes evidence on various Non Pharmacological Cognitive Enhancers such as physical exercise, sleep, meditation and yoga, spirituality, nutrients, computer training, brain stimulation, and music. We also discuss their role in ageing and different neuro-psychiatric disorders, and current status of Cochrane database recommendations. We searched the Pubmed database for the articles and reviews having the terms 'non pharmacological and cognitive' in the title, published from 2000 till 2014. A total of 11 results displayed, out of which 10 were relevant to the review. These were selected and reviewed. Appropriate cross-references within the articles along with Cochrane reviews were also considered and studied. PMID:26393186

  13. Non Pharmacological Cognitive EnhancersCurrent Perspectives

    PubMed Central

    Kumar, Kuldip; Anand, Kuljeet Singh

    2015-01-01

    Cognition refers to the mental processes involved in thinking, knowing, remembering, judging, and problem solving. Cognitive dysfunctions are an integral part of neuropsychiatric disorders as well as in healthy ageing. Cognitive Enhancers are molecules that help improve aspects of cognition like memory, intelligence, motivation, attention and concentration. Recently, Non Pharmacological Cognitive Enhancers have gained popularity as effective and safe alternative to various established drugs. Many of these Non Pharmacological Cognitive Enhancers seem to be more efficacious compared to currently available Pharmacological Cognitive Enhancers. This review describes and summarizes evidence on various Non Pharmacological Cognitive Enhancers such as physical exercise, sleep, meditation and yoga, spirituality, nutrients, computer training, brain stimulation, and music. We also discuss their role in ageing and different neuro-psychiatric disorders, and current status of Cochrane database recommendations. We searched the Pubmed database for the articles and reviews having the terms ‘non pharmacological and cognitive’ in the title, published from 2000 till 2014. A total of 11 results displayed, out of which 10 were relevant to the review. These were selected and reviewed. Appropriate cross-references within the articles along with Cochrane reviews were also considered and studied. PMID:26393186

  14. Microstructures and critical currents in high-{Tc} superconductors

    SciTech Connect

    Suenaga, Masaki

    1998-11-01

    Microstructural defects are the primary determining factors for the values of critical-current densities in a high {Tc} superconductor after the electronic anisotropy along the a-b plane and the c-direction. A review is made to assess firstly what would be the maximum achievable critical-current density in YBa{sub 2}Cu{sub 3}O{sub 7} if nearly ideal pinning sites were introduced and secondly what types of pinning defects are currently introduced or exist in YBa{sub 2}Cu{sub 3}O{sub 7} and how effective are these in pinning vortices.

  15. Current Pulses Momentarily Enhance Thermoelectric Cooling

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey; Fleurial, Jean-Pierre; Caillat, Thierry; Chen, Gang; Yang, Rong Gui

    2004-01-01

    The rates of cooling afforded by thermoelectric (Peltier) devices can be increased for short times by applying pulses of electric current greater than the currents that yield maximum steady-state cooling. It has been proposed to utilize such momentary enhancements of cooling in applications in which diode lasers and other semiconductor devices are required to operate for times of the order of milliseconds at temperatures too low to be easily obtainable in the steady state. In a typical contemplated application, a semiconductor device would be in contact with the final (coldest) somewhat taller stage of a multistage thermoelectric cooler. Steady current would be applied to the stages to produce steady cooling. Pulsed current would then be applied, enhancing the cooling of the top stage momentarily. The principles of operation are straightforward: In a thermoelectric device, the cooling occurs only at a junction at one end of the thermoelectric legs, at a rate proportional to the applied current. However, Joule heating occurs throughout the device at a rate proportional to the current squared. Hence, in the steady state, the steady temperature difference that the device can sustain increases with current only to the point beyond which the Joule heating dominates. If a pulse of current greater than the optimum current (the current for maximum steady cooling) is applied, then the junction becomes momentarily cooled below its lowest steady temperature until thermal conduction brings the resulting pulse of Joule heat to the junction and thereby heats the junction above its lowest steady temperature. A theoretical and experimental study of such transient thermoelectric cooling followed by transient Joule heating in response to current pulses has been performed. The figure presents results from one of the experiments. The study established the essential parameters that characterize the pulse cooling effect, including the minimum temperature achieved, the maximum

  16. Measurement of critical current for bulk superconductors by transport method

    NASA Astrophysics Data System (ADS)

    Kikegawa, T. S.; Sasaki, H.; Tada, H.; Kudo, T.; Kikuchi, H.; Konno, K.; Muralidhar, M.; Murakami, M.; Noto, K.; Awaji, S.; Watanabe, K.

    2005-10-01

    The method of critical current measurement in a magnetic field using a DC transport current has been developed for bulk superconductors. The measurement of the critical current, Ic, up to 50 A at a temperature of 77 K became possible by reducing thermal and mechanical stresses caused in the sample due to rapid cooling from the room temperature to 77 K and a electromagnetic force (Lorentz force), etc. The critical current of 50 A is reduced into 14,000 A/cm 2 of critical current density, Jc, with a cross section of 0.0035 cm 2. The magnetic field dependence of Jc was investigated from 1 T to 10 T for (Nd 0.33Eu 0.38Gd 0.28)Ba 2Cu 3O y bulk superconductors. The magnetization measurement was performed for the sample cut out from the same part of the same crystal as that used for the transport measurement of Ic, from which the critical current density was also estimated. In low magnetic fields, the magnitude of critical current density obtained by the transport method, JcT, was larger than that estimated from the magnetization, JcM. This result reflects the difference of criterion to determine the value of JcT and JcM. In higher magnetic fields, however, it was observed that JcT was smaller than JcM and the irreversibility field estimated from JcT- B curve is slightly lower than that given by the magnetic hysteresis. When the external magnetic field was applied, anomalous voltage peaks in the I- V curve were observed below IcT, which may be caused by the sample slightly moving by the Lorentz force.

  17. Critical current destabilizing perpendicular magnetization by the spin Hall effect

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tomohiro; Mitani, Seiji; Hayashi, Masamitsu

    2015-07-01

    The critical current needed to destabilize the magnetization of a perpendicular ferromagnet via the spin Hall effect is studied. Both the dampinglike and fieldlike torques associated with the spin current generated by the spin Hall effect are included in the Landau-Lifshitz-Gilbert equation to model the system. In the absence of the fieldlike torque, the critical current is independent of the damping constant and is much larger than that of conventional spin torque switching of collinear magnetic systems, as in magnetic tunnel junctions. With the fieldlike torque included, we find that the critical current scales with the damping constant as α0 (i.e., damping independent), α , and α1 /2 depending on the sign of the fieldlike torque and other parameters such as the external field. Numerical and analytical results show that the critical current can be significantly reduced when the fieldlike torque possesses the appropriate sign, i.e., when the effective field associated with the fieldlike torque is pointing opposite to the spin direction of the incoming electrons. These results provide a pathway to reducing the current needed to switch magnetization using the spin Hall effect.

  18. Setup for fast-pulsed measurements of large critical currents

    NASA Astrophysics Data System (ADS)

    D'Ovidio, Claudio Alberto; Esparza, Daniel Antonio; Malachevsky, Maria Teresa

    2000-07-01

    We describe a set of equipments for pulsed measurements of transport critical currents in superconducting materials having a critical current of tens or hundreds of amperes. It is based on the appliance of an electrical current for a very short period of time, rapid enough to preserve the integrity of the current leads and to minimize the Joule effect. Power is applied to the wire-sample setup and the voltage drop is measured within seconds, with a resolution of the order of 10 nV. In this way the I- V characteristics can be obtained with a 1% error, if the 1 μV/ cm criterion is employed. The hardware is composed of three parts: the current pulse generator, a fast low-noise voltage amplifier and a PC with a DAC-ADC card. The data acquisition is achieved via an Assembler program.

  19. Scaling rules for critical current density in anisotropic biaxial superconductors

    NASA Astrophysics Data System (ADS)

    Li, Yingxu; Kang, Guozheng; Gao, Yuanwen

    2016-06-01

    Recent researches highlight the additional anisotropic crystallographic axis within the superconducting plane of high temperature superconductors (HTS), demonstrating the superconducting anisotropy of HTS is better understood in the biaxial frame than the previous uniaxial coordinates within the superconducting layer. To quantitatively evaluate the anisotropy of flux pinning and critical current density in HTS, we extend the scaling rule for single-vortex collective pinning in uniaxial superconductors to account for flux-bundle collective pinning in biaxial superconductors. The scaling results show that in a system of random uncorrected point defects, the field dependence of the critical current density is described by a unified function with the scaled magnetic field of the isotropic superconductor. The obtained angular dependence of the critical current density depicts the main features of experimental observations, considering possible corrections due to the strong-pinning interaction.

  20. Electromigration kinetics and critical current of Pb-free interconnects

    SciTech Connect

    Lu, Minhua; Rosenberg, Robert

    2014-04-07

    Electromigration kinetics of Pb-free solder bump interconnects have been studied using a single bump parameter sweep technique. By removing bump to bump variations in structure, texture, and composition, the single bump sweep technique has provided both activation energy and power exponents that reflect atomic migration and interface reactions with fewer samples, shorter stress time, and better statistics than standard failure testing procedures. Contact metallurgies based on Cu and Ni have been studied. Critical current, which corresponds to the Blech limit, was found to exist in the Ni metallurgy, but not in the Cu metallurgy. A temperature dependence of critical current was also observed.

  1. Critical Current Measurements in Commercial Tapes, Coils, and Magnets.

    NASA Astrophysics Data System (ADS)

    Gubser, D. U.; Soulen, R. J., Jr.; Fuller-Mora, W. W.; Francavilla, T. L.

    1996-03-01

    We have measured a number of tapes, coils, and magnets produced by commercial vendors and determined their properties as functions of magnetic field and temperature. The tapes were measured at the National High Magnetic Field Laboratory in magnetic fields to 20 tesla and at temperatures of 4.2 K, 27 K, 65 K, and 77 K. For the tapes we report critical currents and current-voltage characteristics. Six inch diameter coils were measured at NRL in zero magnetic field. Critical currents, current-voltage characteristics, and reliability studies are reported for the coils. Larger 10 inch diameter coils, which are to be used in a 200 hp superconducting motor, were also measured and results will be presented. The talk will also review the status of the most recent tests of the superconducting motor.

  2. Bolstering medical education to enhance critical care capacity in Cambodia.

    PubMed

    Albert, Tyler J; Fassier, Thomas; Chhuoy, Meng; Bounchan, Youttiroung; Tan, Sokhak; Ku, No; Chhor, Nareth; LoGerfo, James P; West, T Eoin

    2015-04-01

    The capacity to care for the critically ill has long been viewed as a fundamental element of established and comprehensive health care systems. Extending this capacity to health care systems in low- and middle-income countries is important given the burden of disease in these regions and the significance of critical care in overall health system strengthening. However, many practicalities of improving access and delivery of critical care in resource-limited settings have yet to be elucidated. We have initiated a program to build capacity for the care of critically ill patients in one low-income Southeast Asian country, Cambodia. We are leveraging existing international academic partnerships to enhance postgraduate critical care education in Cambodia. After conducting a needs assessment and literature review, we developed a three-step initiative targeting training in mechanical ventilation. First, we assessed and revised the current resident curriculum pertaining to mechanical ventilation. We addressed gaps in training, incorporated specific goals and learning objectives, and decreased the hours of lectures in favor of additional bedside training. Second, we are incorporating e-learning, e-teaching, and e-assessment into the curriculum, with both live, interactive and independent, self-paced online instruction. Third, we are developing a train-the-trainer program defined by bidirectional international faculty exchanges to provide hands-on, case-based, and bedside training to achieve competency-based outcomes. In targeting specific educational needs and a key population-the next generation of Cambodian intensivists-this carefully designed approach should address some existing gaps in the health care system and hopefully yield a lasting impact. PMID:25751194

  3. Apparatus for measurement of critical current in superconductive tapes

    SciTech Connect

    Coulter, J. Yates; DePaula, Raymond

    2002-01-01

    A cryogenic linear positioner which is primarily used for characterizing coated conductor critical current homogeneity at 75K is disclosed. Additionally, this tool can be used to measure the positional dependence of the coated conductor resistance at room temperature, and the room temperature resistance of the underlying YBCB coating without the overlaying protective cover of silver.

  4. Critical currents and dissipative effects in proton-irradiated ceramic YBCO and BISCO

    SciTech Connect

    Mezzetti, E.; Minetti, B. ); Andreone, D. ); Cherubini, R. ); Gherardi, L.; Metra, P. )

    1992-04-01

    Transport properties in pellets of YBCO and BISCO are studied before and after 6.5-MeV proton implantation. The average critical current was strongly enhanced but in one case also weakened, probably due to the unfavorable interaction with the pre-irradiation defect structure. Characteristic parameters are compared and discussed. 17 refs., 3 figs.

  5. Critical Josephson current in the dynamical Coulomb blockade regime

    NASA Astrophysics Data System (ADS)

    Jäck, Berthold; Eltschka, Matthias; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R.; Kern, Klaus

    2016-01-01

    The current-voltage characteristics of a voltage-biased Josephson junction in the low conductance regime of an ultra-low temperature scanning tunneling microscope (STM) is dominated by sequential charge tunneling. Using P (E ) theory we show that the Josephson coupling energy, experimentally determined in this regime, is in good agreement with the critical current I0 calculated from the Ambegaokar-Baratoff formula. In this way, we can determine the critical current values of a Josephson junction in an STM. Furthermore, we experimentally determine a range of validity for P (E ) theory, which is in accordance with theoretical predictions. In this way, we establish an optimal parameter range, in which Josephson STM can be performed.

  6. Magnetically modulated critical current densities of Co/Nb hybrid

    NASA Astrophysics Data System (ADS)

    Li, Zhigang; Wang, Weike; Zhang, Li; Yang, Zhaorong; Tian, Mingliang; Zhang, Yuheng

    2015-12-01

    By tuning morphology and size of magnetic subsystem, ferromagnet-superconductor (F/S) hybrid system provides an effective way to modulate superconductivity due to the interaction between superconducting and magnetic-order parameters at the mesoscopic length scale. In this work, we report on investigations of critical current density in a large-area Co/Nb hybrid via facile colloidal lithography. Here, Co hexagon shell array as a magnetic template build on Nb film to modulate the critical current density. A novel superconducting transition has been observed in I-V curve with two metastable transition states: double-transition and binary-oscillation-transition states. Importantly, such unusual behavior can be adjusted by temperature, magnetic field and contact area of F/S. Such hybrid film has important implications for understanding the role of magnetic subsystem modulating superconductivity, as well as applied to low-energy electronic devices such as superconducting current fault limiters.

  7. Magnetically modulated critical current densities of Co/Nb hybrid

    PubMed Central

    Li, Zhigang; Wang, Weike; Zhang, Li; Yang, Zhaorong; Tian, Mingliang; Zhang, Yuheng

    2015-01-01

    By tuning morphology and size of magnetic subsystem, ferromagnet-superconductor (F/S) hybrid system provides an effective way to modulate superconductivity due to the interaction between superconducting and magnetic-order parameters at the mesoscopic length scale. In this work, we report on investigations of critical current density in a large-area Co/Nb hybrid via facile colloidal lithography. Here, Co hexagon shell array as a magnetic template build on Nb film to modulate the critical current density. A novel superconducting transition has been observed in I-V curve with two metastable transition states: double-transition and binary-oscillation-transition states. Importantly, such unusual behavior can be adjusted by temperature, magnetic field and contact area of F/S. Such hybrid film has important implications for understanding the role of magnetic subsystem modulating superconductivity, as well as applied to low-energy electronic devices such as superconducting current fault limiters. PMID:26678595

  8. Topographically Enhanced Subinertial Currents at Endeavour Ridge

    NASA Astrophysics Data System (ADS)

    Thomson, R. E.; Rabinovich, A. B.; Mihaly, S. F.; Veirs, S.; Stahr, F. R.; McDuff, R. E.; Subbotina, M. M.

    2001-12-01

    We use velocity records collected from moored current meters to examine the effects of seafloor topography and hydrothermal venting on near-bottom (\\~ 2000 m depth) currents flowing over the Endeavour Segment of Juan de Fuca Ridge. Focus is on the 50-m vertical resolution records collected from July-October 2000 near the main Endeavour vent field and on the 2-km lateral resolution records collected from July-October 2001 at three sites within the 100 m deep axial valley. Semidiurnal currents are found to be marginally more energetic than diurnal currents, and flow above the ridge crest is often dominated by wind-generated inertial events (periods \\~ 16 hrs at 48N) and low-frequency (O(10 day) period) clockwise rotary motions. Observations, supported by numerical modeling, reveal marked topographic amplification of subinertial motions within 100 m of the ridge crest. Motions within the diurnal, inertial, and wind-forced frequency bands undergo especially pronounced above-ridge amplification but attenuate equally rapidly within the confines of the narrow (\\~ 1 km) axial valley. Semidiurnal currents are much less affected by the ridge topography and have approximately uniform amplitudes with depth within the first 250 m of the bottom. Within a few tens of meters of the valley floor, the flow is dominated by \\~ 5 cm/s along-axis semidiurnal oscillations and a surprisingly strong (2 to 4 cm/s), persistently northward up-valley flow. The up-valley flow appears to be independent of, and generally counter to, the prevailing flow in the overlying water column. Initial findings suggest that the enhanced near-bottom flow is maintained by an along-valley pressure gradient created by turbulent entrainment of cold (\\~ 2 C) ambient water by the superheated (\\~ 350 C) hydrothermal plumes and low-temperature diffuse flow. If so, the mean-flow dynamics may be analogous to the summer sea-breeze in coastal fjords, with hydrothermal convection playing the role of summertime

  9. Critical current of laminated and non-laminated BSCCO superconducting composite tape under bending strain

    NASA Astrophysics Data System (ADS)

    Matsubayashi, H.; Mukai, Y.; Arai, T.; Shin, J. K.; Ochiai, S.; Okuda, H.; Osamura, K.; Otto, A.; Malozemoff, A.

    2009-10-01

    It has been reported that, when the (Bi,Pb) 2Sr 2Ca 2Cu 3O x (hereafter noted as BSCCO)/Ag/Ag-alloy tape is laminated with stainless steel, the tensile strain tolerance of critical current is much improved. In this study, using the non-laminated and laminated BSCCO composite tapes fabricated at American Superconductor Corporation, the influences of lamination on the critical current and its distribution under bending strain were studied. The analysis of the measured variation of average critical current with bending strain based on the damage evolution model revealed that the laminated stainless steel acts to suppress the fracture of the BSCCO filaments. The experimentally observed high critical current retention of the laminated tape up to high bending strain was accounted for by the suppression of fracture of BSCCO filaments stated above and enhancement of the compressive residual strain in the filaments. The distributions of local critical current in non-laminated and laminated composite tape were described well by the three-parameter Weibull distribution function within the bending strain lower than 1.1%. The coefficient of variation of distribution of critical current of the laminated tape was similar to that of the non-laminated one under the same strain distribution in the core.

  10. Online Scenarios in FCS College Courses: Enhancing Critical Thinking Skills

    ERIC Educational Resources Information Center

    Martin, Lynda; Thompson, Stacy D.; Richards, Lynne

    2008-01-01

    Critical thinking is a vital skill for higher education students. The Virtual Exchange was created by the authors to provide instructors with a unique approach to helping students enhance their critical thinking skills. Pilot data were collected from three universities where instructors used Virtual Exchange scenarios in their courses in different…

  11. Using the Enhanced Critical Incident Technique in Counselling Psychology Research

    ERIC Educational Resources Information Center

    Butterfield, Lee D.; Borgen, William A.; Maglio, Asa-Sophia T.; Amundson, Norman E.

    2009-01-01

    This article describes an effective approach to using the Enhanced Critical Incident Technique (ECIT) research method based on Flanagan's (1954) Critical Incident Technique (CIT). It begins with an overview of the CIT, how to decide if it is the appropriate methodology to use, then, using a recent CIT study as an example, discusses Flanagan's five…

  12. Critical current density and flux pinning in an unconventional superconductor

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Kaul, S. N.; Rodríguez Fernández, J.; Fernández Barquín, L.

    2009-12-01

    The functional dependence of the critical current density on magnetic field, J(H), observed at fixed temperatures in the unconventional type-II superconductor, LaAgMn ( c=0.1,0.2,0.3) alloys, but not the relative magnitude of J in different alloy compositions at any given temperature and field, is adequately described by the exponential-decay critical state model. In accordance with the predictions of the Kramer's flux-pinning model, the peak value of the pinning force density FPmax∝( with the exponent 1.7⩽m⩽2.8 and F/FPmax scales with h=H/Hc_2, where Hc_2 is the upper critical field. Irrespective of sample composition and temperature in the superconducting state, the pinning of the flux line lattice (FLL) dominates over the plastic FLL shear.

  13. Critical current density in railgrun accelerators with composite electrodes

    SciTech Connect

    Stankevich, S.V.; Shvetsov, G.A.

    1995-11-01

    The present paper is intended to study the possibilities of increasing the critical current density in railgun accelerators using composite electrodes of various structure. Before proceeding to the analysis this way, it should be noted that the requirements for materials selected for the rails go beyond the values of the current density. In real practice account should be taken of the technological problems concerned with the production of the electrodes, as well as of those concerned with the railgun performance, including the multishot life.

  14. Thin-film Josephson junctions with alternating critical current density

    NASA Astrophysics Data System (ADS)

    Moshe, Maayan; Kogan, V. G.; Mints, R. G.

    2009-01-01

    We study the field dependence of the maximum current Im(H) in narrow edge-type thin-film Josephson junctions with alternating critical current density. Im(H) is evaluated within nonlocal Josephson electrodynamics taking into account the stray fields that affect the difference of the order-parameter phases across the junction and therefore the tunneling currents. We find that the phase difference along the junction is proportional to the applied field, depends on the junction geometry, but is independent of the Josephson critical current density gc , i.e., it is universal. An explicit form for this universal function is derived for small currents through junctions of the width W≪Λ , the Pearl length. The result is used to calculate Im(H) . It is shown that the maxima of Im(H)∝1/H and the zeros of Im(H) are equidistant but only in high fields. We find that the spacing between zeros is proportional to 1/W2 . The general approach is applied to calculate Im(H) for a superconducting quantum interference device with two narrow edge-type junctions. If gc changes sign periodically or randomly, as it does in grain boundaries of high- Tc materials and superconductor-ferromagnet-superconductor heterostructures, Im(H) not only acquires the major side peaks, but due to nonlocality the following peaks decay much slower than in bulk junctions.

  15. Mapping the current-current correlation function near a quantum critical point

    NASA Astrophysics Data System (ADS)

    Prodan, Emil; Bellissard, Jean

    2016-05-01

    The current-current correlation function is a useful concept in the theory of electron transport in homogeneous solids. The finite-temperature conductivity tensor as well as Anderson's localization length can be computed entirely from this correlation function. Based on the critical behavior of these two physical quantities near the plateau-insulator or plateau-plateau transitions in the integer quantum Hall effect, we derive an asymptotic formula for the current-current correlation function, which enables us to make several theoretical predictions about its generic behavior. For the disordered Hofstadter model, we employ numerical simulations to map the current-current correlation function, obtain its asymptotic form near a critical point and confirm the theoretical predictions.

  16. Enhancing critical thinking in clinical practice: implications for critical and acute care nurses.

    PubMed

    Shoulders, Bridget; Follett, Corrinne; Eason, Joyce

    2014-01-01

    The complexity of patients in the critical and acute care settings requires that nurses be skilled in early recognition and management of rapid changes in patient condition. The interpretation and response to these events can greatly impact patient outcomes. Nurses caring for these complex patients are expected to use astute critical thinking in their decision making. The purposes of this article were to explore the concept of critical thinking and provide practical strategies to enhance critical thinking in the critical and acute care environment. PMID:24895950

  17. Magnesium boride superconductors: Processing, characterization and enhancement of critical fields

    NASA Astrophysics Data System (ADS)

    Bhatia, Mohit

    In this work, the basic formation of in-situ MgB2, and how variations in the formation process influence the electrical and magnetic properties of this material was studied. Bulk MgB2 samples were prepared by stoichiometric, elemental powder mixing and compaction followed by heat-treatment. Strand samples were prepared by a modified powder-in-tube technique with subsequent heat-treatment. The influence of various heat-treatment schedules on the formation reaction was studied. Two different optimum heat-treatment windows were indentified, namely, low-temperature heat-treatment (below the melting point of Mg i.e. between 620--650°C) and high-temperature heat-treatment (>650°C) for the preparation of MgB2 with good transport properties. XRD was used to confirm phase formation and microstructural variations were studied with the help of SEM. Following a study of the reaction temperature regimes, the focus turned to critical field enhancement via doping with various compounds targeting either the Mg or the B sites. The effects of these dopants on the superconducting properties, in particular the critical fields, were studied. Large increases in irreversibility field, muoH irr, and upper critical field, Bc2, of bulk and strand superconducting MgB2 were achieved by separately adding SiC, amorphous C, and selected metal diborides (NaB2, ZrB 2, TiB2) in bulk samples and three different sizes of SiC (˜200 nm, 30 nm and 15 nm) in strand samples. Lattice spacing shifts and resistivity measurements (on some samples) were consistent with dopant introduction to the lattice. It was also found that both muoH irr and Bc2 depend on the sensing current level which may be an indication of current path percolations. These increases in the Bc2 were also complimented by an increase in the transport Jcs, especially for the SiC doped samples. It was important to differentiate between the effects on the transport properties arising from possible particulate enhanced flux pinning from that

  18. Stock markets and criticality in the current economic crisis

    NASA Astrophysics Data System (ADS)

    da Silva, Roberto; Zembrzuski, Marcelo; Correa, Fabio C.; Lamb, Luis C.

    2010-12-01

    We show that the current economic crisis has led the market to exhibit a non-critical behavior. We do so by analyzing the quantitative parameters of time series from the main assets of the Brazilian Stock Market BOVESPA. By monitoring global persistence we show a deviation of power law behavior during the crisis in a strong analogy with spin systems (from where this concept was originally conceived). Such behavior is corroborated by an emergent heavy tail of absolute return distribution and also by the magnitude autocorrelation exponent. Comparisons with universal exponents obtained in the international stock markets are also performed. This suggests how a thorough analysis of suitable exponents can bring a possible way of forecasting market crises characterized by non-criticality.

  19. Enhancement of critical heat flux in tubes using staged tangential flow injection: (Progress report)

    SciTech Connect

    Dhir, V.K.

    1987-01-01

    Experimental studies of the enhancement in single and two phase heat transfer from tubes subjected to tangential flow injection have been continuing. Investigations using water as the test liquid have been focused on: single phase heat transfer coefficients; two phase heat transfer coefficients under subcooled boiling conditions; subcooled critical heat fluxes; and modeling of the enhancement under swirl flow conditions. With tangential injection up to four fold increase in the average heat transfer coefficient has been observed. During subcooled boiling the enhancement is relatively small. However swirl induced centripetal force increases vapor escape velocity and as a result higher critical heat fluxes can be accommodated. In the range of flow parameters studied up to 40% enhancement in critical heat flux has been observed with single stage injection. This enhancement is slightly less than that obtained with Freon-113. The mechanistic reasons for this observation are currently being investigated.

  20. Enhancement of critical heat flux in tubes using staged tangential flow injection

    NASA Astrophysics Data System (ADS)

    Dhir, V. K.

    Experimental studies of the enhancement in single and two phase heat transfer from tubes subjected to tangential flow injection have been continuing. Investigations using water as the test liquid have been focused on: single phase heat transfer coefficients; two phase heat transfer coefficients under subcooled boiling conditions; subcooled critical heat fluxes; and modeling of the enhancement under swirl flow conditions. With tangential injection up to four fold increase in the average heat transfer coefficient has been observed. During subcooled boiling the enhancement is relatively small. However swirl induced centripetal force increases vapor escape velocity and as a result higher critical heat fluxes can be accommodated. In the range of flow parameters studied up to 40% enhancement in critical heat flux has been observed with single stage injection. This enhancement is slightly less than that obtained with Freon-113. The mechanistic reasons for this observation are currently being investigated.

  1. Persistent Currents and Quantum Critical Phenomena in Mesoscopic Physics

    NASA Astrophysics Data System (ADS)

    Zelyak, Oleksandr

    In this thesis, we study persistent currents and quantum critical phenomena in the systems of mesoscopic physics. As an introduction in Chapter 1 we familiarize the reader with the area of mesoscopic physics. We explain how mesoscopic systems are different from quantum systems of single atoms and molecules and bulk systems with an Avogadro number of elements. We also describe some important mesoscopic phenomena. One of the mathematical tools that we extensively use in our studies is Random Matrix Theorty. This theory is not a part of standard physics courses and for educational purposes we provide the basics of Random Matrix Theory in Chapter 2. In Chapter 3 we study the persistent current of noninteracting electrons in quantum billiards. We consider simply connected chaotic Robnik-Berry quantum billiard and its annular analog. The electrons move in the presence of a point-like magnetic flux at the center of the billiard. For the simply connected billiard, we find a large diamagnetic contribution to the persistent current at small flux, which is independent of the flux and is proportional to the number of electrons (or equivalently the density since we keep the area fixed). The size of this diamagnetic contribution is much larger than the previously studied mesoscopic fluctuations in the persistent current in the simply connected billiard. This behavior of persistent current can ultimately be traced to the response of the angular-momentum l = 0 levels (neglected in semiclassical expansions) on the unit disk to a point-like flux at its center. We observe the same behavior for the annular billiard when the inner radius is much smaller than the outer one. We also find that the usual fluctuating persistent current and Anderson-like localization due to boundary scattering are seen when the annulus tends to a one-dimensional ring. We explore the conditions for the observability of this phenomenon. In Chapter 4 we study quantum critical phenomena in a system of two

  2. Flux creep and critical currents in oxide superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, T.

    1990-06-01

    The non-dissipative current that superconductors can carry in the presence of a magnetic field originates from pinning interactions between fluxoids and inhomogeneities in superconductors called pinning centers. However, the non-dissipative persistent current decays logarithmically in time due to a thermal activation of fluxoids trapped in pinning potentials, i.e., the flux creep. It happens also that the critical current density ( Jc), the maximum density of the non-dissipative current is even reduced to zero at high magnetic fields. The boundary between zero and nonzero Jcs in the temperature-magnetic field plane is called the irreversibility line. The effects of the flux creep on the irreversibility line and the decreasing rate of the persistent current are quantitatively investigated in association with the strength of the flux pinning. A discussion is given on the possibility of application of oxide superconductors at liquid nitrogen temperature. The correlation between the broad resistive transition in oxide superconductors and the flux creep is also discussed.

  3. Ketamine: Current applications in anesthesia, pain, and critical care

    PubMed Central

    Kurdi, Madhuri S.; Theerth, Kaushic A.; Deva, Radhika S.

    2014-01-01

    Ketamine was introduced commercially in 1970 with the manufacturer's description as a “rapidly acting, nonbarbiturate general anesthetic” and a suggestion that it would be useful for short procedures. With the help of its old unique pharmacological properties and newly found beneficial clinical properties, ketamine has survived the strong winds of time, and it currently has a wide variety of clinical applications. It's newly found neuroprotective, antiinflammatory and antitumor effects, and the finding of the usefulness of low dose ketamine regimens have helped to widen the clinical application profile of ketamine. The present article attempts to review the current useful applications of ketamine in anesthesia, pain and critical care. It is based on scientific evidence gathered from textbooks, journals, and electronic databases. PMID:25886322

  4. Doubling the critical current density of high temperature superconducting coated conductors through proton irradiation

    SciTech Connect

    Jia, Y.; LeRoux, M.; Miller, D. J.; Wen, J. G.; Kwok, W. K.; Welp, U.; Rupich, M. W.; Li, X.; Sathyamurthy, S.; Fleshler, S.; Malozemoff, A. P.; Kayani, A.; Ayala-Valenzuela, O.; Civale, L.

    2013-09-16

    The in-field critical current of commercial YBa{sub 2}Cu{sub 3}O{sub 7} coated conductors can be substantially enhanced by post-fabrication irradiation with 4 MeV protons. Irradiation to a fluence of 8 × 10{sup 16} p/cm{sup 2} induces a near doubling of the critical current in fields of 6 T || c at a temperature of 27 K, a field and temperature range of interest for applications, such as rotating machinery. A mixed pinning landscape of preexisting precipitates and twin boundaries and small, finely dispersed irradiation induced defects may account for the improved vortex pinning in high magnetic fields. Our data indicate that there is significant head-room for further enhancements.

  5. Critical Current Oscillations of Josephson Junctions with Ferromagnetic Layers

    NASA Astrophysics Data System (ADS)

    Glick, Joseph A.; Khasawneh, Mazin A.; Niedzielski, Bethany M.; Loloee, Reza; Pratt, W. P., Jr.; Birge, Norman O.

    Josephson junctions containing ferromagnetic layers are of considerable interest for the development of practical cryogenic memory and superconducting qubits. Such junctions exhibit a phase shift of π for certain ranges of ferromagnetic layer thickness. We present studies of Nb based micron-scale Josephson junctions using ferromagnetic layers of Ni, Ni81Fe19, or Ni65Co20Fe15. By applying an external magnetic field, the critical current of the junctions containing Ni81Fe19 and Ni65Co20Fe15 is found to follow a characteristic Fraunhofer pattern, and displays the clear switching behavior expected of single-domain magnets. However, the junctions containing Ni exhibit more complex behaviors. The maximum value of the critical current, extracted from the Fraunhofer patterns, oscillates as a function of the ferromagnetic layer thickness, indicating transitions in the phase difference across the junction between values of zero and π. We compare the data to previous work and to models of the 0- π transitions based on existing clean and dirty limit theories. This work was supported by IARPA via ARO Contract W911NF-14-C-0115.

  6. Hysteresis in Transport Critical-Current Measurements of Oxide Superconductors

    PubMed Central

    Goodrich, L. F.; Stauffer, T. C.

    2001-01-01

    We have investigated magnetic hysteresis in transport critical-current (Ic) measurements of Ag-matrix (Bi,Pb)2Sr2Ca2Cu3O10–x (Bi-2223) and AgMg-matrix Bi2Sr2CaCu2O8+x (Bi-2212) tapes. The effect of magnetic hysteresis on the measured critical current of high temperature superconductors is a very important consideration for every measurement procedure that involves more than one sweep of magnetic field, changes in field angle, or changes in temperature at a given field. The existence of this hysteresis is well known; however, the implications for a measurement standard or interlaboratory comparisons are often ignored and the measurements are often made in the most expedient way. A key finding is that Ic at a given angle, determined by sweeping the angles in a given magnetic field, can be 17 % different from the Ic determined after the angle was fixed in zero field and the magnet then ramped to the given field. Which value is correct is addressed in the context that the proper sequence of measurement conditions reflects the application conditions. The hysteresis in angle-sweep and temperature-sweep data is related to the hysteresis observed when the field is swept up and down at constant angle and temperature. The necessity of heating a specimen to near its transition temperature to reset it to an initial state between measurements at different angles and temperatures is discussed. PMID:27500042

  7. Internally oxidized Nb₃Sn strands with fine grain size and high critical current density.

    PubMed

    Xu, Xingchen; Sumption, Michael D; Peng, Xuan

    2015-02-25

    Nb3Sn strands fabricated using Nb-Zr alloy can be internally oxidized, provided that oxygen is properly supplied via an oxide powder. This allows the formation of fine intragranular and intergranular ZrO2 particles in a Nb3Sn matrix. These particles can refine the grain size by a factor of three and thereby greatly enhance the Nb3Sn critical current density. PMID:25582555

  8. Giant increase in critical current density of KxFe2-ySe₂ single crystals

    DOE PAGESBeta

    Lei, Hechang; Petrovic, C.

    2011-12-28

    The critical current density Jabc of KxFe2-ySe₂ single crystals can be enhanced by more than one order of magnitude, up to ~2.1×10⁴ A/cm² by the post annealing and quenching technique. A scaling analysis reveals the universal behavior of the normalized pinning force as a function of the reduced field for all temperatures, indicating the presence of a single vortex pinning mechanism. The main pinning sources are three-dimensional (3D) point-like normal cores. The dominant vortex interaction with pinning centers is via spatial variations in critical temperature Tc (“δTc pinning”).

  9. Critical current density and current distribution in field cooled superconducting disks

    NASA Astrophysics Data System (ADS)

    Bernstein, Pierre; Noudem, Jacques; Dupont, Louis

    2016-07-01

    Applications of bulk superconductors concern superconducting motors and generators, the levitation of vehicles, the generation of high magnetic fields with small size cryo-magnets, the shielding of magnetic fields and other applications. For all of them, it is essential to determine the critical current density, and to understand the effect of the shape and size of the bulks on the properties of interest. In this contribution, we show how the combination of levitation force and trapped field measurements allow one to determine the characteristics and the potential performances of superconducting disks using analytical modeling. As examples of applications we detail the effects of the magnetizing field and of the bulk sheet critical current density on the levitation force. An important result of the reported measurements is that in field-cooled samples, the shielding currents possibly do not flow along the whole thickness of the disks.

  10. Microstructural and crystallographic imperfections of MgB{sub 2} superconducting wire and their correlation with the critical current density

    SciTech Connect

    Shahabuddin, Mohammed; Alzayed, Nasser S.; Oh, Sangjun; Choi, Seyong; Maeda, Minoru; Hata, Satoshi; Shimada, Yusuke; Hossain, Md Shahriar Al; Kim, Jung Ho

    2014-01-15

    A comprehensive study of the effects of structural imperfections in MgB{sub 2} superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB{sub 2} material are increased, as reflected by detailed X-ray refinement and the normal state resistivity. The crystalline imperfections, caused by lattice disorder, directly affect the impurity scattering between the π and σ bands of MgB{sub 2}, resulting in a larger upper critical field. In addition, low sintering temperature keeps the grain size small, which leads to a strong enhancement of pinning, and thereby, enhanced critical current density. Owing to both the impurity scattering and the grain boundary pinning, the critical current density, irreversibility field, and upper critical field are enhanced. Residual voids or porosities obviously remain in the MgB{sub 2}, however, even at low sintering temperature, and thus block current transport paths.

  11. Caffeine and cardiovascular diseases: critical review of current research.

    PubMed

    Zulli, Anthony; Smith, Renee M; Kubatka, Peter; Novak, Jan; Uehara, Yoshio; Loftus, Hayley; Qaradakhi, Tawar; Pohanka, Miroslav; Kobyliak, Nazarii; Zagatina, Angela; Klimas, Jan; Hayes, Alan; La Rocca, Giampiero; Soucek, Miroslav; Kruzliak, Peter

    2016-06-01

    Caffeine is a most widely consumed physiological stimulant worldwide, which is consumed via natural sources, such as coffee and tea, and now marketed sources such as energy drinks and other dietary supplements. This wide use has led to concerns regarding the safety of caffeine and its proposed beneficial role in alertness, performance and energy expenditure and side effects in the cardiovascular system. The question remains "Which dose is safe?", as the population does not appear to adhere to the strict guidelines listed on caffeine consumption. Studies in humans and animal models yield controversial results, which can be explained by population, type and dose of caffeine and low statistical power. This review will focus on comprehensive and critical review of the current literature and provide an avenue for further study. PMID:26932503

  12. Targeted temperature management: Current evidence and practices in critical care

    PubMed Central

    Saigal, Saurabh; Sharma, Jai Prakash; Dhurwe, Ritika; Kumar, Sanjay; Gurjar, Mohan

    2015-01-01

    Targeted temperature management (TTM) in today's modern era, especially in intensive care units represents a promising multifaceted therapy for a variety of conditions. Though hypothermia is being used since Hippocratic era, the renewed interest of late has been since early 21st century. There have been multiple advancements in this field and varieties of cooling devices are available at present. TTM requires careful titration of its depth, duration and rewarming as it is associated with side-effects. The purpose of this review is to find out the best evidence-based clinical practice criteria of therapeutic hypothermia in critical care settings. TTM is an unique therapeutic modality for salvaging neurological tissue viability in critically ill patients viz. Post-cardiac arrest, traumatic brain injury (TBI), meningitis, acute liver failure and stroke. TTM is standard of care in post-cardiac arrest situations; there has been a lot of controversy of late regarding temperature ranges to be used for the same. In patients with TBI, it reduces intracranial pressure, but has not shown any favorable neurologic outcome. Hypothermia is generally accepted treatment for hypoxic ischemic encephalopathy in newborns. The current available technology to induce and maintain hypothermia allows for precise temperature control. Future studies should focus on optimizing hypothermic treatment to full benefit of our patients and its application in other clinical scenarios. PMID:26430341

  13. Enhancement in the transport critical current density J{sub c} in YBa{sub 2}Cu{sub 3}O{sub 7−δ} added with an insulating nano crystalline YBa{sub 2}HfO{sub 5.5} perovskite

    SciTech Connect

    Rejith, P. P.; Vidya, S.; Thomas, J. K.; Solomon, Sam

    2014-01-28

    When a magnetic field is applied to type II superconductors, such as YBa{sub 2}Cu{sub 3}0{sub 7−δ} (YBCO), the flux quanta penetrate the material as a regular array of vortices. However when transport currents are applied, they act to move these vortices, thus lowers the critical current density (J{sub c}) as well as destroying superconductivity. The development of microstructures made of YBCO materials has enabled engineers to increase the critical current density, within Type II materials by introducing flux pinning centres into the material. The microstructure and flux pinning properties of YBa{sub 2}Cu{sub 3}O{sub 7−δ} system with varying levels (0-5 wt. %) of a nano perovskite ceramic insulator; YBa{sub 2}HfO{sub 5.5} addition was studied in detail. Orthorhombic YBa{sub 2}Cu{sub 3}O{sub 7−δ} powder was prepared through conventional solid state route and a modified combustion method was used for synthesizing nanocrystalline YBa{sub 2}HfO{sub 5.5}. The structure and microstructure of the samples examined by X-ray diffraction and scanning electron microscopy showed that YBa{sub 2}HfO{sub 5.5} and YBCO remained unreacted even at higher processing temperature without deteriorating the superconducting properties. The scanning electron microscope image shows that YBa{sub 2}HfO{sub 5.5} forms an electrical-network between grains. These observations suggest that the YBa{sub 2}HfO{sub 5.5} addition to the Y-123-compounds improve the electrical connection between superconducting grains and substantial improvements in the relative electrical transport properties of the composites. The variation of sintering temperature, density, critical transition temperature (T{sub c}) and magnetic field dependence of critical current density (J{sub c}) of YBa{sub 2}Cu{sub 3}O{sub 7−δ} having different proportions of YBa{sub 2}HfO{sub 5.5} in the matrix were also studied in detail. It is found that the addition of these elements considerably enhances the flux pinning

  14. Low-field critical current density in porous MgB2 powders

    NASA Astrophysics Data System (ADS)

    Agassi, Y. D.

    2013-09-01

    Porous MgB2 powders are comprised of an ensemble of irregularly shaped constituents. In this work we introduce a model for the critical current density in such powders in the presence of a low external field H (H < 4 T) and in the high-porosity limit, where effects of vortex-lattice elasticity can be neglected and vortex pinning takes place within the powder-constituents. The ensuing critical current-density expression is a product of three decoupled factors: The first sets the scale for the critical current-density magnitude, while the second and third factors contain the field and powder-constituent size-parameters dependencies, respectively. The field dependent factor is of the form H-n and 0.5⩽n⩽1.0, where the limiting exponents n = 0.5 and n = 1.0 correspond to vortex configurations within a powder-constituent of a linear array and a two-dimensional lattice, respectively. For the calculations, we assume for the powder constituent shape a cylinder of arbitrary height and radius, where an external field and a single pinned vortex are aligned in parallel to the cylinder’s axis. The exact fields of this configuration are derived. The size-parameters dependence implies enhanced critical current density for a cigar-like shape powder-constituent aligned with the field, and of radius smaller than about three times the penetration depth. These conclusions are consistent with pertaining data.

  15. Current trends in developing medical students' critical thinking abilities.

    PubMed

    Harasym, Peter H; Tsai, Tsuen-Chiuan; Hemmati, Payman

    2008-07-01

    Health care is fallible and prone to diagnostic and management errors. The major categories of diagnostic errors include: (1) no-fault errors--the disease is present but not detected; (2) system errors--a diagnosis is delayed or missed because of the imperfection in the health care system; and (3) cognitive errors--a misdiagnosis from faulty data collection or interpretation, flawed reasoning, or incomplete knowledge. Approximately one third of patient problems are mismanaged because of diagnostic errors. Part of the solution lies in improving the diagnostic skills and critical thinking abilities of physicians as they progress through medical school and residency training. However, this task is challenging since both medical problem-solving and the learning environments are complex and not easily understood. There are many interacting variables including the motivation of the medical student (e.g. deep versus surface learning), the acquisition and evolution of declarative and conditional knowledge (e.g. reduced, dispersed, elaborated, scheme, and scripted), problem-solving strategies (e.g. procedural knowledge-guessing, hypothetical deductive, scheme inductive, and pattern recognition), curricular models (e.g. apprenticeship, discipline-based, body system-based, case-based, clinical presentation-based), teaching strategies (e.g. teaching general to specific or specific to general), the presented learning opportunities (PBL versus scheme inductive PBL), and the nature of the learning environment (e.g. modeling critical thinking and expert problem-solving). This paper elaborates on how novices differ from experts and how novices can be educated in a manner that enhances their level of expertise and diagnostic abilities as they progress through several years of medical training. PMID:18805749

  16. Magnetic field dependence of critical currents in superconducting polycrystals

    SciTech Connect

    Kugel, K.I.; Lisovskaya, T.Y. ); Mints, R.G. )

    1992-02-10

    The authors study the dependence of critical current j{sub c} on magnetic field H in superconducting polycrystals which are considered as system of superconducting crystallites (isotropic or anisotropic) with Josephson contacts between them. Isotropy or anisotropy of contacts depends on the orientation of their crystallographic axes relatively to edges of contact planes. In this paper it is shown that for a system of randomly oriented isotropic contacts, the dependence j{sub c}(H) in a relatively wide field range has the asymptotic form j{sub c} {approximately} (InH)/H{sup 2}. This differs drastically from j{sub c}(H) for single contacts. Anisotropy effects due to large differences in London penetration depth {lambda} values corresponding to external magnetic field directed along different axes are analyzed in detail. It is shown that for uniaxal crystals with {lambda}{sub 1} = {lambda}{sub 2} {lt} {lambda}{sub 3}, this anisotropy leads to the relation j{sub c} {approximately} {radical}{lambda}{sub 3}/{lambda}{sub 1} for chaotic orientation of crystallites. The form of j{sub c}(H) curves for two different orientations of the magnetic field relatively to the transport current through the sample is found.

  17. Enhancement of pumped current in quantum dots

    NASA Astrophysics Data System (ADS)

    Ramos, Juan Pablo; Foa, Luis; Apel, Victor Marcelo; Orellana, Pedro

    A direct current usually requires the application of a non-zero potential difference between source and drain, but on nanoscale systems (NSS) it is possible to obtain a non-zero current while the potential difference is zero. The effect is known as quantum charge pumping (QCP) and it is due to the interference provided by the existence of a time-dependent potential (TDP). QCP can be generated by a TDP in non-adiabatic limit. An example of this is a system composed by a ring with a dot embedded on it, under the application of an oscillating TDP. By the action of a magnetic field across the system, a pumped current is generated, since time reversal symmetry is broken. Decoherence is crucial, both from a scientific and technological point of view. In NSS it is expected that decoherence, among others things, decreases the QCP amplitude. In this context, we study what is the effect of a bath on the pumped current in our system. We find that for certain values of magnetic flux, the bath-system produce amplification of the pumped current.

  18. Current anti-doping policy: a critical appraisal

    PubMed Central

    Kayser, Bengt; Mauron, Alexandre; Miah, Andy

    2007-01-01

    Background Current anti-doping in competitive sports is advocated for reasons of fair-play and concern for the athlete's health. With the inception of the World Anti Doping Agency (WADA), anti-doping effort has been considerably intensified. Resources invested in anti-doping are rising steeply and increasingly involve public funding. Most of the effort concerns elite athletes with much less impact on amateur sports and the general public. Discussion We review this recent development of increasingly severe anti-doping control measures and find them based on questionable ethical grounds. The ethical foundation of the war on doping consists of largely unsubstantiated assumptions about fairness in sports and the concept of a "level playing field". Moreover, it relies on dubious claims about the protection of an athlete's health and the value of the essentialist view that sports achievements reflect natural capacities. In addition, costly antidoping efforts in elite competitive sports concern only a small fraction of the population. From a public health perspective this is problematic since the high prevalence of uncontrolled, medically unsupervised doping practiced in amateur sports and doping-like behaviour in the general population (substance use for performance enhancement outside sport) exposes greater numbers of people to potential harm. In addition, anti-doping has pushed doping and doping-like behaviour underground, thus fostering dangerous practices such as sharing needles for injection. Finally, we argue that the involvement of the medical profession in doping and anti-doping challenges the principles of non-maleficience and of privacy protection. As such, current anti-doping measures potentially introduce problems of greater impact than are solved, and place physicians working with athletes or in anti-doping settings in an ethically difficult position. In response, we argue on behalf of enhancement practices in sports within a framework of medical supervision

  19. Critical Ethnography in Education: Origins, Current Status, and New Directions.

    ERIC Educational Resources Information Center

    Anderson, Gary L.

    The development of critical ethnography in education is traced, and the central epistemological and methodological issues in the practice of critical ethnography are discussed. Some of the directions the field appears to be taking are considered. Critical ethnography in education began in the late 1960's and early 1970's, with roots in the…

  20. Ethical debates: enhancing critical thinking in nursing students.

    PubMed

    Candela, Lori; Michael, Susan Rush; Mitchell, Shae

    2003-01-01

    The use of classroom debates can be helpful in teaching ethical content that is often nebulous and difficult for students to comprehend and apply. Debates enhance critical thinking skills through researching issues and developing a stance that can be supported in scientific literature. The authors describe a student debate project involving ethical issues with chronically ill clients. Many students changed their views during the debates. Students evaluated the debates as a positive learning experience. PMID:12544615

  1. Vibration effect on magnetization and critical current density of superconductors

    NASA Astrophysics Data System (ADS)

    Golovchanskiy, Igor A.; Pan, Alexey V.; George, Jonathan; Wells, Frederick S.; Fedoseev, Sergey A.; Rozenfeld, Anatoly

    2016-07-01

    In this work the effect of vibrations on critical current density (J c ) of superconductors has been studied. The vibrations are shown to affect J c of all types of superconductors during their measurements, employing a vibrating sample magnetometer (VSM). Increasing vibration frequency (f) and/or amplitude (A) leads to progressive reduction of J c as a function of magnetic field (B a ). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on {J}c({B}a) curves. Analysis of magnetization loops and relaxation of magnetization in YBCO films revealed that the vibration effect can be treated as the effective reduction of pinning potential. The asymmetry of the vibration effect in ascending and descending B a is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A are shown to have rather insignificant influence, while the vibrational vortex dynamics exhibit a strong impact. The irreversibility field ({B}{{irr}}) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of {B}{{irr}} for J c modeling is demonstrated.

  2. Management of polycythaemia vera: a critical review of current data.

    PubMed

    McMullin, Mary F; Wilkins, Bridget S; Harrison, Claire N

    2016-02-01

    Polycythaemia vera (PV) is a chronic blood cancer; its clinical features are dominated by myeloproliferation (erythrocytosis, often leucocytosis and/or thrombocytosis) and a tendency for thrombosis and transformation to myelofibrosis or acute myeloid leukaemia. In the past 10 years the pathophysiology of this condition has been defined as JAK/STAT pathway activation, almost always due to mutations in JAK2 exons 12 or 14 (JAK2 V617F). In the same time period our understanding of the optimal management of PV has expanded, most recently culminating in the approval of JAK inhibitors for the treatment of PV patients who are resistant or intolerant to therapy with hydroxycarbamide. It has also been demonstrated that life expectancy for many patients with PV is not normal, nor is their quality of life. We critically explore these findings and discuss their impact. In addition, we highlight persisting gaps in our current management strategy; for example, what is the optimal first line cytoreductive therapy and, indeed, which patients need cytoreductive drugs. PMID:26492433

  3. Critical current density and trapped field in HTS with asymmetric magnetization loops

    NASA Astrophysics Data System (ADS)

    Gokhfeld, D.

    2016-03-01

    Applications of the extended critical state model are considered. The trapped magnetic field, the penetration field and the field dependence of the critical current density are analysed. The critical current density and the trapped field in superconducting grains depend on the grain size. Asymmetry of the hysteresis curves relative to the M = 0 axis is related to the scale of the current circulation.

  4. Current and Future Critical Issues in Rocket Propulsion Systems

    NASA Technical Reports Server (NTRS)

    Navaz, Homayun K.; Dix, Jeff C.

    1998-01-01

    The objective of this research was to tackle several problems that are currently of great importance to NASA. In a liquid rocket engine several complex processes take place that are not thoroughly understood. Droplet evaporation, turbulence, finite rate chemistry, instability, and injection/atomization phenomena are some of the critical issues being encountered in a liquid rocket engine environment. Pulse Detonation Engines (PDE) performance, combustion chamber instability analysis, 60K motor flowfield pattern from hydrocarbon fuel combustion, and 3D flowfield analysis for the Combined Cycle engine were of special interest to NASA. During the summer of 1997, we made an attempt to generate computational results for all of the above problems and shed some light on understanding some of the complex physical phenomena. For this purpose, the Liquid Thrust Chamber Performance (LTCP) code, mainly designed for liquid rocket engine applications, was utilized. The following test cases were considered: (1) Characterization of a detonation wave in a Pulse Detonation Tube; (2) 60K Motor wall temperature studies; (3) Propagation of a pressure pulse in a combustion chamber (under single and two-phase flow conditions); (4) Transonic region flowfield analysis affected by viscous effects; (5) Exploring the viscous differences between a smooth and a corrugated wall; and (6) 3D thrust chamber flowfield analysis of the Combined Cycle engine. It was shown that the LTCP-2D and LTCP-3D codes are capable of solving complex and stiff conservation equations for gaseous and droplet phases in a very robust and efficient manner. These codes can be run on a workstation and personal computers (PC's).

  5. Measurement of the critical current and transient characteristics of a high-temperature superconductor tube using a pulsed current supply.

    SciTech Connect

    Cha, Y. S.

    1998-08-27

    The transient response of a melt-cast-processed BSCCO-2212 superconductor tube is investigated by using a pulsed current source. It was found that (1) the maximum induced current and the excitation current at field penetration increase with the maximum excitation current, and (2) there is a time delay between peak excitation current and peak magnetic field inside the superconductor. These observations can be explained by the concept of magnetic diffusion. The ac steady-state critical current of the superconductor was found to depend on the magnitude of the current increment. The critical current determined by using the pulsed current system agrees fairly well with the ac steady-state critical current determined by using relatively large current increment.

  6. Criticisms of Higher Education: Picturesque Exaggerations Found in Current Writings.

    ERIC Educational Resources Information Center

    Eells, Walter Crosby

    1979-01-01

    Extracts from the recent flood of criticism of the American college and university are presented from a wide variety of sources. Topics of criticism include faculty, students, curriculum, athletics, teaching methods, alumni, and college aims. (Article originally published in 1934.) (AF)

  7. Recent R&D progress on DI-BSCCO wires with high critical current properties

    NASA Astrophysics Data System (ADS)

    Kagiyama, Tomohiro; Kobayashi, Shin-ichi; Yamazaki, Kouhei; Kikuchi, Masashi; Yamade, Satoru; Nakashima, Takayoshi; Hayashi, Kazuhiko; Sato, Ken-ichi; Shimoyama, Jun-ichi; Kitaguchi, Hitoshi

    Sumitomo Electric has been developing the silver-sheathed Bi2223 multi-filamentary wires since the discovery of Bi-based superconductors. DI-BSCCO is the superconducting wire with high and uniform critical current properties produced using the controlled-overpressure (CT-OP) sintering technique. The present commercial DI-BSCCO can provide the uniform high critical current, Ic, up to 180 A with length over 2000 m, and recently over 200 A with length over 1000 m were produced successfully, resulting from the improvement and control of the microstructure in Bi2223 multi-filaments. The short trial wires of several meters have exhibited the highest Ic over 240 A at 77 K in self-field (corresponding to 580 A per 1 cm-width). Besides, the optimization of carrier density after CT-OP have led to further enhancement of Ic, reached 250 A at 77 K in self-field. All the derivative products also have uniform critical current properties over entire length even after lamination with the reinforcing metals. The performances of DI-BSCCO can meet the growing needs for various applications of high temperature superconductor like high in-field applications, such as magnets and motors. The recent progress in transport properties of commercial DI-BSCCO and R&D short trial wires is shown.

  8. Criticality safety enhancements for SCALE 6.2 and beyond

    SciTech Connect

    Rearden, Bradley T.; Bekar, Kursat B.; Celik, Cihangir; Clarno, Kevin T.; Dunn, Michael E.; Hart, Shane W.; Ibrahim, Ahmad M.; Johnson, Seth R.; Langley, Brandon R.; Lefebvre, Jordan P.; Lefebvre, Robert A.; Marshall, William J.; Mertyurek, Ugur; Mueller, Don; Peplow, Douglas E.; Perfetti, Christopher M.; Petrie Jr, Lester M.; Thompson, Adam B.; Wiarda, Dorothea; Wieselquist, William A.; Williams, Mark L.

    2015-01-01

    SCALE is a widely used suite of tools for nuclear systems modeling and simulation that provides comprehensive, verified and validated, user-friendly capabilities for criticality safety, reactor physics, radiation shielding, and sensitivity and uncertainty analysis. Since 1980, regulators, industry, and research institutions around the world have relied on SCALE for nuclear safety analysis and design. SCALE 6.2 provides several new capabilities and significant improvements in many existing features for criticality safety analysis. Enhancements are realized for nuclear data; multigroup resonance self-shielding; continuous-energy Monte Carlo analysis for sensitivity/uncertainty analysis, radiation shielding, and depletion; and graphical user interfaces. An overview of these capabilities is provided in this paper, and additional details are provided in several companion papers.

  9. Polycrystalline Superconducting Thin Films: Texture Control and Critical Current Density

    NASA Astrophysics Data System (ADS)

    Yang, Feng

    1995-01-01

    The growth processes of polycrystalline rm YBa_2CU_3O_{7-X} (YBCO) and yttria-stabilized-zirconia (YSZ) thin films have been developed. The effectiveness of YSZ buffer layers on suppression of the reaction between YBCO thin films and metallic substrates was carefully studied. Grown on the chemically inert surfaces of YSZ buffer layers, YBCO thin films possessed good quality of c-axis alignment with the c axis parallel to the substrate normal, but without any preferred in-plane orientations. This leads to the existence of a large percentage of the high-angle grain boundaries in the YBCO films. The critical current densities (rm J_{c}'s) found in these films were much lower than those in single crystal YBCO thin films, which was the consequence of the weak -link effect of the high-angle grain boundaries in these films. It became clear that the in-plane alignment is vital for achieving high rm J_{c }s in polycrystalline YBCO thin films. To induce the in-plane alignment, ion beam-assisted deposition (IBAD) technique was integrated into the conventional pulsed laser deposition process for the growth of the YSZ buffer layers. It was demonstrated that using IBAD the in-plane orientations of the YSZ grains could be controlled within a certain range of a common direction. This ion -bombardment induced in-plane texturing was explained using the anisotropic sputtering yield theory. Our observations and analyses have provided valuable information on the optimization of the IBAD process, and shed light on the texturing mechanism in YSZ. With the in-plane aligned YSZ buffer layers, YBCO thin films grown on metallic substrates showed improved rm J_{c}s. It was found that the in-plane alignment of YSZ and that of YBCO were closely related. A direct correlation was revealed between the rm J_{c} value and the degree of the in-plane alignment for the YBCO thin films. To explain this correlation, a numerical model was applied to multi-grain superconducting paths with different

  10. Enhancement of Thermally Injected Spin Current through an Antiferromagnetic Insulator.

    PubMed

    Lin, Weiwei; Chen, Kai; Zhang, Shufeng; Chien, C L

    2016-05-01

    We report a large enhancement of thermally injected spin current in normal metal (NM)/antiferromagnet (AF)/yttrium iron garnet (YIG), where a thin AF insulating layer of NiO or CoO can enhance the spin current from YIG to a NM by up to a factor of 10. The spin current enhancement in NM/AF/YIG, with a pronounced maximum near the Néel temperature of the thin AF layer, has been found to scale linearly with the spin-mixing conductance at the NM/YIG interface for NM=3d, 4d, and 5d metals. Calculations of spin current enhancement and spin mixing conductance are qualitatively consistent with the experimental results. PMID:27203336

  11. Enhancement of Thermally Injected Spin Current through an Antiferromagnetic Insulator

    NASA Astrophysics Data System (ADS)

    Lin, Weiwei; Chen, Kai; Zhang, Shufeng; Chien, C. L.

    2016-05-01

    We report a large enhancement of thermally injected spin current in normal metal (NM)/antiferromagnet (AF)/yttrium iron garnet (YIG), where a thin AF insulating layer of NiO or CoO can enhance the spin current from YIG to a NM by up to a factor of 10. The spin current enhancement in NM /AF /YIG , with a pronounced maximum near the Néel temperature of the thin AF layer, has been found to scale linearly with the spin-mixing conductance at the NM /YIG interface for NM =3 d , 4 d , and 5 d metals. Calculations of spin current enhancement and spin mixing conductance are qualitatively consistent with the experimental results.

  12. Critical current anisotropy in Nd-1111 single crystals and the influence of neutron irradiation

    NASA Astrophysics Data System (ADS)

    Eisterer, M.; Mishev, V.; Zehetmayer, M.; Zhigadlo, N. D.; Katrych, S.; Karpinski, J.

    2014-04-01

    We report on angle-resolved magnetization measurements on NdFeAsO0.65F0.35 (Nd-1111) single crystals. The field dependence of the critical current density, Jc, is non-monotonic in these crystals at all orientations and temperatures due to the fishtail effect, which strongly influences the angular dependence of Jc. The currents decrease as the field is tilted from the crystallographic c-axis at low fields, but increase at high fields. A peak occurs in the angular dependence of Jc at intermediate fields. The critical currents are significantly enhanced after irradiation with fast neutrons and the fishtail disappears. The different current anisotropies at low and high fields, however, persist. We discuss the data in the framework of the anisotropic scaling approach and propose a transition from dominant pinning by large defects of low density at low fields to pinning by small defects of high density at high fields in the pristine crystal. Strong pinning dominates at all fields after the irradiation, and the angular dependence of Jc can be described via anisotropic scaling only after an appropriate extension to this pinning regime.

  13. Critical current and flux pinning properties of the superconducting Ti-V alloys

    NASA Astrophysics Data System (ADS)

    Matin, Md.; Sharath Chandra, L. S.; Chattopadhyay, M. K.; Meena, R. K.; Kaul, Rakesh; Singh, M. N.; Sinha, A. K.; Roy, S. B.

    2015-05-01

    We present a study on the critical current density and the flux-line pinning properties of a series of annealed and as cast samples of Ti100-xVx (x = 20, 30, 40 and 60) alloys, performed with the help of magnetization measurements. We show that the grain boundaries are the dominant flux pinning centers in the Ti-V alloys in the low and intermediate magnetic field regime. In the high magnetic field regime, the dislocation networks and the point pinning mechanism provided by the ω phase present in these alloys are more effective than the grain boundaries. While in the low magnetic fields we find the signature of surface effects enhancing the pinning force density, a peak effect in the critical current is observed in these alloys in the high field regime near the upper critical field HC2. Using the existing theories we provide an analysis of the pinning force density over a large range of magnetic fields, and obtain some new insight on the influence of various metallurgical phases, grain boundaries and dislocation networks on the flux-line pinning properties of these alloys.

  14. Stable superconducting magnet. [high current levels below critical temperature

    NASA Technical Reports Server (NTRS)

    Boom, R. W. (Inventor)

    1967-01-01

    Operation of a superconducting magnet is considered. A method is described for; (1) obtaining a relatively high current in a superconducting magnet positioned in a bath of a gas refrigerant; (2) operating a superconducting magnet at a relatively high current level without training; and (3) operating a superconducting magnet containing a plurality of turns of a niobium zirconium wire at a relatively high current level without training.

  15. Computer Assisted Instruction: Current Trends and Critical Issues.

    ERIC Educational Resources Information Center

    Chambers, Jack A.; Sprecher, Jerry W.

    1980-01-01

    The use of computers to assist in learning situations is reviewed on an international basis, evaluation studies and costs are examined, and critical issues are analyzed as they pertain to hardware, software, and courseware development. Recommendations are offered for educationally cost-effective uses of computer-assisted instruction. A 67-item…

  16. Postgraduate Research Supervision: A Critical Review of Current Practice

    ERIC Educational Resources Information Center

    McCallin, Antoinette; Nayar, Shoba

    2012-01-01

    Changes in the funding and delivery of research programmes at the university level have, in recent years, resulted in significant changes to research supervision. This paper critically reviews key influences effecting postgraduate supervision. Analysis draws on literature spanning 2000-2010 to determine the appropriateness of traditional models of…

  17. Change of the V I curve and critical current with applied tensile strain due to cracking of filaments in Bi2223 composite tape

    NASA Astrophysics Data System (ADS)

    Shin, J. K.; Ochiai, S.; Okuda, H.; Sugano, M.; Oh, S. S.

    2008-11-01

    The critical current at 77 K of multifilamentary Bi2223 composite tape was studied under applied tensile strain experimentally and analytically. Beyond the irreversible strain, the critical currents (IC) decreased significantly with increasing applied tensile strain (ɛc), due to the enhanced cracking of the Bi2223 filaments. The voltage generation in the voltage-current relation was calculated by the current share model in which the transport current is shared by the Bi2223 filament and Ag near the cracked portion. Then the critical current was estimated with a 1 µV cm-1 criterion. By the application of the current share model to the experimental result, the effective crack length responsible for the reduction in critical current was estimated, with which the change of critical current could be described satisfactorily as a function of applied strain.

  18. Critical Current Properties in Longitudinal Magnetic Field of YBCO Superconductor with APC

    NASA Astrophysics Data System (ADS)

    Kido, R.; Kiuchi, M.; Otabe, E. S.; Matsushita, T.; Jha, A. K.; Matsumoto, K.

    The critical current density (Jc) properties of the Artificial Pinning Center (APC) introduced YBa2Cu3O7 (YBCO) films in the longitudinal magnetic field were measured. Y2O3 or Y2BaCuO5 (Y211) was introduced as APCs to YBCO, and YBCO films with APC were fabricated on SrTiO3 single crystal substrate. The sizes of Y2O3 and Y211 were 5-10 nm and 10-20 nm, respectively. As a result, Jc enhancement in the longitudinal magnetic field was observed in Y2O3 introduced YBCO films. However, it was not observed in Y211 introduced YBCO films. Therefore, it was considered that Jc properties in the longitudinal magnetic field were affected by introducing of small size APC, and it was necessary that APC does not disturb the current pathway in the superconductor.

  19. Enhancement of critical current density of YBa2Cu3O7-x thin films by self-assembly of Y2O3 nanoparticles

    SciTech Connect

    Vishwanathan, S.; Gapud, Albert Agcaoili; Varela del Arco, Maria; Abiade, J.; Christen, David K; Pennycook, Stephen J; Kumar, Dhananjay

    2007-01-01

    YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) thin films, possessing high critical current density (J{sub c}), have been synthesized by embedding a homogeneous array of Y2O3 non-superconducting nanoclusters/nanoparticles using a pulsed laser deposition technique. The size, interparticle spacing, and density of Y2O3 nanoparticles in YBCO thin films were tailored by varying the number of laser pulses in order to determine the optimum size for effective immobilization of vortices. Scanning transmission electron microscopy with atomic number contrast and X-ray diffraction techniques were used to determine the size and structure of the nanoparticles. Both techniques indicate that the Y{sub 2}O{sub 3} particles are epitaxial with respect to the surrounding YBCO matrix. The information about pinning of vortices by the nanoparticles was obtained by investigating the behavior of critical current density as a function of temperature and applied field, which in turn determines the vortex density in the sample. The superconducting transition temperature ({Tc}) of YBCO films with the inclusion of nanoparticles was observed to remain almost the same or decrease marginally (1-2 K) with respect to Tc of pure YBCO films deposited under identical conditions. However, JcS of YBCO films embedded with self-assembled nanoparticles were found to be significantly higher than that of pure YBCO films. The Jc enhancement was up to five times in high magnetic field, which is a key requirement for practical application of high-{Tc} materials.

  20. Raising Relational Critical Consciousness to Enhance Empathy in Clinical Hypnosis.

    PubMed

    Vargas, H Luis

    2016-01-01

    Empathic involvement theory suggests that a trance-like experience occurs when a cross-relational empathic connection is achieved. The empathically-laden relational phenomenon is thought to enhance hypnosis. Empathic involvement theory suggests hypnotizables are highly empathic. By the same token, the relational empathic connection necessitates a highly empathic practitioner of hypnosis. In the United States, where values of individualism are thought to be socially embedded and internalized, practitioners of hypnosis and clients alike may be impeded by an individually oriented worldview to empathically connect with others. Raising a relational critical consciousness is promoted as a way to increase sensitivity to the marginalization of relationships, limit empathic-effort burn-out, and promote cross-relational empathic connection. PMID:26675156

  1. Current diagnosis and treatments for critical congenital heart defects

    PubMed Central

    ZENG, ZHANDONG; ZHANG, HONGWEI; LIU, FENGLI; ZHANG, NING

    2016-01-01

    Congenital heart defects (CHD) affect approximately 7% of infants, and account for 3% of all infant deaths. CHD is most often caused by the defects associated with ductus arteriosus, which is a vessel that usually closes shortly after birth. The types of CHD include tetralogy of fallot, hypoplastic left heart syndrome, pulmonary atresia, total anomalous pulmonary venous return, transposition of great arteries, tricuspid atresia and truncus arteriosus. There are some risk factors that can increase the chance of a fetus developing CHD such as prematurity, an existing CHD in a first-degree relative, genetic syndromes, infections in utero, maternal drug consumptions and disorders. CHD is diagnosed is through different techniques including pulse oximetry, echocardiograms and physical exams. In this review, we examined the current incidence of CHD, the risk factors associated with CHD, the current methods of diagnosis and surgical options used to repair the defects. PMID:27168772

  2. Recent R&D progress on DI-BSCCO wires with high critical current properties

    NASA Astrophysics Data System (ADS)

    Nakashima, T.; Kobayashi, S.; Kagiyama, T.; Yamazaki, K.; Kikuchi, M.; Yamade, S.; Hayashi, K.; Sato, K.; Shimoyama, J.; Kitaguchi, H.; Kumakura, H.

    2011-11-01

    Sumitomo Electric has been developing the silver-sheathed Bi2223 multi-filamentary wires since the discovery of Bi-based superconductors. DI-BSCCO is the high performance wires produced with the controlled-overpressure (CT-OP) sintering technique. The present commercial DI-BSCCO can provide the uniform high critical current, I c, up to 180 A over 2000 m, and recently 200 A were succeeded to obtain with the same kind of 1000 m-long wires, resulting from the improvement and control of the microstructure in Bi2223 multi-filaments. The short trial wires of several meter have exhibited over 240 A as the highest I c at 77 K, self-field (corresponding to 580 A per 1 cm-width) according with high T c over 112 K. Besides, the optimization of carrier density after CT-OP led to further enhancement of I c, reaching 250 A. All the derivative products have also uniform critical current property over the entire length even after lamination with the reinforcements. The performances of DI-BSCCO can meet the growing needs for various high temperature superconducting applications involving high in-field properties, such as magnets and motors. The recent progress on I c including in-field properties along with the remarkable findings on the performances of DI-BSCCO will be shown.

  3. Rapid Doubling of the Critical Current of YBa2Cu3O7-δ Coated Conductors

    NASA Astrophysics Data System (ADS)

    Welp, U.; Leroux, M.; Kihlstrom, K. J.; Holleis, S.; Rupich, M. W.; Sathyamurthy, S.; Fleshler, S.; Sheng, H. P.; Miller, D. J.; Eley, S.; Civale, L.; Niraula, P. M.; Kayani, A.; Kwok, W. K.

    We demonstrate the doubling of the critical current density of production-line REBCO coated conductors (CCs) in fields of 6 T ||c at 27 K by irradiation with a 3.5-MeV oxygen ion beam. This doubling of Jc is achieved within one second or less opening an industrially viable approach to address a persisting challenge, namely the greatly reduced performance of CCs in even modest applied magnetic fields. TEM images reveal that the enhanced critical current is due to finely dispersed small clusters approximately 5 nm in diameter. The major effect of the irradiation-induced defects is the reduction of the field-dependence of Jc, which we attribute to the mixed pinning landscape composed of strong pre-existing pin sites and the finely dispersed irradiation-induced defects. Work supported by the Center for Emergent Superconductivity, an EFRC funded by the U.S. Department of Energy, Office of Basic Energy Sciences. Patterning and microstructural characterization were performed at the Center for Nanoscale Materials, an Office of Science user facility, supported by the Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  4. Doubling of the Critical Current Density of 2G-YBCO Coated Conductors through proton irradiation

    NASA Astrophysics Data System (ADS)

    Welp, Ulrich; Jia, Ying; Kwok, Wai-Kwong; Rupich, Marty; Fleshler, Steven; Kayani, Asfghar

    2013-03-01

    We report on magnetization and transport measurements of the critical current density of commercial 2G YBCO coated conductors before and after proton irradiation. The samples were irradiated along the c-axis with 4 MeV protons to a fluence of 1.5x1016 p/cm2. We find that at temperatures below 50 K, proton irradiation increases Jc by a factor of 2 in low fields and increases up to 2.5 in fields of 7 T. At 77 K, proton irradiation is less effective in enhancing the critical current. Doubling of Jc in fields of several Tesla and at temperatures below 50 K will be highly beneficial for applications of coated conductors in rotating machinery, generators and magnet coils. - Work supported by the US DoE-BES funded Energy Frontier Research Center (YJ), and by Department of Energy, Office of Science, Office of Basic Energy Sciences (UW, WKK), under Contract No. DE-AC02-06CH11357.

  5. The effect of self field on the critical current determination of multifilamentary superconductors

    SciTech Connect

    Garber, M.; Ghosh, A.K.; Sampson, W.B.

    1988-01-01

    In determining the short sample critical current of conductors of large cross section or high current density the self field produced by the transport current must be taken account in order to obtain a ''true value'' for the critical current. A simple model calculation for determining this effect is described. Measurements on wires, cables, and monoliths show the validity and self consistency of the procedures. 9 refs., 13 figs., 1 tab.

  6. The critical current of point symmetric Josephson tunnel junctions

    NASA Astrophysics Data System (ADS)

    Monaco, Roberto

    2016-06-01

    The physics of Josephson tunnel junctions drastically depends on their geometrical configurations. The shape of the junction determines the specific form of the magnetic-field dependence of its Josephson current. Here we address the magnetic diffraction patterns of specially shaped planar Josephson tunnel junctions in the presence of an in-plane magnetic field of arbitrary orientations. We focus on a wide ensemble of junctions whose shape is invariant under point reflection. We analyze the implications of this type of isometry and derive the threshold curves of junctions whose shape is the union or the relative complement of two point symmetric plane figures.

  7. Multiple-element eddy current probes for enhanced inspection

    SciTech Connect

    Clark, W.G. Jr. )

    1993-07-01

    Eddy current inspection methods are widely used for the nondestructive evaluation (NDE) of tubular products. Specifically, the sensors and instrumentation are designed to detect and characterize changes in a material's electrical and magnetic properties produced by the presence of discontinuities. A recent major enhancement in eddy current inspection technology has been the development of computer interfacing for data collection, analysis, and display. This breakthrough has led to multiple-frequency testing, eddy current imaging, and automated data interpretation systems that significantly enhance both capabilities and reliability of the eddy current inspection. In addition to the clear advantages in data processing, computer interfacing also permits the design and creation of unique sensors that further enhance eddy current inspection capabilities. Perhaps the most promising area of computer interactive probe design is multiple element sensors. Westinghouse engineers and scientists have pioneered this area of probe development. This paper describes four unique probes that illustrate the advantages of computer interactive multiple element sensors for additional eddy current inspection options.

  8. Improved critical current in confined superconductors in parallel field configuration

    NASA Astrophysics Data System (ADS)

    Glatz, Andreas; Aronson, Igor; Wang, Yonglei; Xiao, Zhili

    2015-03-01

    We present results on the re-entrance of the superconducting state in systems placed into a magnetic field parallel to the applied current. In experiments it was observed that the magneto-resistance first increases with magnetic field, but at higher field drops again such that superconductivity is recovered. This effect is strongly temperature dependent and can lead to a suppression of resistance below the measurable threshold over a range of a few kG. We study the vortex dynamics and magneto-resistance in this situation in the framework of a large-scale time-dependent Ginzburg Landau simulation. A small external current as well as the magnetic field are applied in the x-direction, the latter is then ramped up. Our simulations reproduce this effect and reveal the mechanism for the observed behavior: the intermediate resistive state is due to a vortex instability leading to an unwinding of twisted vortex configurations. This leads to a periodic dynamic resistive state. When the field increases these instabilities get stabilized due to a higher vortex density and the resistance drops upon increasing the magnetic field. Work was supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences, and by the Office of Science, Materials Sc.

  9. Current Status of Mycotoxin Analysis: A Critical Review.

    PubMed

    Shephard, Gordon S

    2016-07-01

    It is over 50 years since the discovery of aflatoxins focused the attention of food safety specialists on fungal toxins in the feed and food supply. Since then, analysis of this important group of natural contaminants has advanced in parallel with general developments in analytical science, and current MS methods are capable of simultaneously analyzing hundreds of compounds, including mycotoxins, pesticides, and drugs. This profusion of data may advance our understanding of human exposure, yet constitutes an interpretive challenge to toxicologists and food safety regulators. Despite these advances in analytical science, the basic problem of the extreme heterogeneity of mycotoxin contamination, although now well understood, cannot be circumvented. The real health challenges posed by mycotoxin exposure occur in the developing world, especially among small-scale and subsistence farmers. Addressing these problems requires innovative approaches in which analytical science must also play a role in providing suitable out-of-laboratory analytical techniques. PMID:27455927

  10. Enhancement of the Bootstrap Current in a Tokamak Pedestal

    SciTech Connect

    Kagan, Grigory; Catto, Peter J.

    2010-07-23

    The strong radial electric field in a subsonic tokamak pedestal modifies the neoclassical ion parallel flow velocity, as well as the radial ion heat flux. Existing experimental evidence of the resulting alteration in the poloidal flow of a trace impurity is discussed. We then demonstrate that the modified parallel ion flow can noticeably enhance the pedestal bootstrap current when the background ions are in the banana regime. Only the coefficient of the ion temperature gradient drive term is affected. The revised expression for the pedestal bootstrap current is presented. The prescription for inserting the modification into any existing banana regime bootstrap current expression is given.

  11. Analysis of distribution of critical current of bent-damaged Bi2223 composite tape

    NASA Astrophysics Data System (ADS)

    Ochiai, S.; Okuda, H.; Sugano, M.; Hojo, M.; Osamura, K.; Kuroda, T.; Kumakura, H.; Kitaguchi, H.; Itoh, K.; Wada, H.

    2011-10-01

    Distributions of critical current of damaged Bi2223 tape specimens bent by 0.6, 0.8 and 1.0% were investigated analytically with a modelling approach based on the correlation of damage evolution to distribution of critical current. It was revealed that the distribution of critical current is described by three parameter Weibull distribution function through the distribution of the tensile damage strain of Bi2223 filaments that determines the damage front in bent-composite tape. Also it was shown that the measured distribution of critical current values can be reproduced successfully by a Monte Carlo simulation using the distributions of tensile damage strain of filaments and original critical current.

  12. Current status of treatments for dyslexia: critical review.

    PubMed

    Alexander, Ann W; Slinger-Constant, Anne-Marie

    2004-10-01

    The acquisition of reading is a complex neurobiologic process. Identifying the most effective instruction and remedial intervention methods for children at risk of developing reading problems and for those who are already struggling is equally complex. This article aims to provide the clinician with a review of more current findings on the prevention and remediation of reading problems in children, along with an approach to considering the diagnosis and treatment of a child with dyslexia. The first part of the review describes interventions targeted at preventing reading difficulties in the at-risk younger child. The second part of the review discusses the efficacy of approaches to treat the older, reading-disabled child ("intervention studies"). Factors that impact the response to treatment are also discussed, as are neuroimaging studies that offer insight into how the brain responds to treatment interventions. With appropriate instruction, at-risk readers can become both accurate and fluent readers. In contrast, although intensive, evidence-based remedial interventions can markedly improve reading accuracy in older, reading-disabled children, they have been significantly less effective in closing the fluency gap. Owing to the dynamic course of language development and the changes in language demands over time, even after a child has demonstrated a substantial response to treatment interventions, his or her subsequent progress should be carefully tracked to ensure optimal progress toward the development of functional reading and written language skills. PMID:15559890

  13. The influence of critical current density of Bi-2212 superconductors by defects after Yb-doping

    NASA Astrophysics Data System (ADS)

    Lu, Tianni; Zhang, Cuiping; Guo, Shengwu; Wu, Yifang; Li, Chengshan; Zhou, Lian

    2015-12-01

    Bi2Sr2Ca1-xYbxCu2O8+δ (Bi-2212) single crystals with x = 0.000, 0.005, 0.010 and 0.020 have been prepared by self-flux method. The influences of Yb doping on the formation of the dislocations in the lattice structures, as well as the related current carrying capability are investigated. Due to the SQUID measurement and the Bean model calculation, the maximum critical current density (Jc) is obtained when the Yb doping content is x = 0.010, though the Tc and the carrier concentration are not in the optimal region. Based on the HRTEM analyses of the Ca-O and Cu-O2 layers, the optimal dislocation density in the Cu-O2 layers is deduced according to the number of the dislocations per unit area. Besides, the sizes of the dislocations also prove the effectiveness of Yb substitution on the enhancement of the current carrying capability in Bi-2212 single crystals.

  14. Dipolar field effects on the critical current for spin transfer switch of iron and permalloy nanoelements

    SciTech Connect

    Oliveira, L. L.; Dantas, J. T. S.; Souza, R. M.; Carriço, A. S.; Dantas, Ana L.

    2014-05-07

    We report a theoretical study of dipolar effects on the switching current density of soft ferromagnetic elliptical nanoelements. Relevant changes on the critical current value are found according to the orientation of the magnetization and the spin polarization with the major axis. We show that the critical current density may be reduced by as much as 92% for thin nanoelements magnetized along the minor axis direction, using in-plane spin polarization parallel to the magnetization.

  15. A Critical Test of Self-Enhancement, Exposure, and Self-Categorization Explanations for First- and Third-Person Perceptions

    ERIC Educational Resources Information Center

    Reid, Scott A.; Byrne, Sahara; Brundidge, Jennifer S.; Shoham, Mirit D.; Marlow, Mikaela L.

    2007-01-01

    The third-person perception is the tendency for people to believe that others are more influenced by media content than themselves (W. P. Davison, 1983). The current study provides a critical test of self-enhancement, exposure, and self-categorization explanations for first- (i.e., self more influenced than others) and third-person perceptions.…

  16. Improved micromorph tandem cell performance through enhanced top cell currents

    SciTech Connect

    Platz, R.; Vaucher, N.P.; Fischer, D.; Meier, J.; Shah, A.

    1997-12-31

    Two approaches to increasing the current in the amorphous silicon top cell of an amorphous silicon/microcrystalline silicon (a-Si:H/{micro}c-Si:H) tandem cell are presented. The goal is to raise the stabilized efficiency of such cells. The deposition of the amorphous top cell at higher than standard substrate temperature is shown to reduce the optical gap of the i-layer and to increase the current which is generated with a given i-layer thickness. Furthermore, a selectively reflecting ZnO interface layer between the component cells is presented as a viable tool for enhancing the current generation in the top cell by selective reflection of light. The authors present a micromorph tandem cell containing the amorphous top cell deposited at high substrate temperature, and additionally the ZnO mirror layer. A top cell thickness of 150 nm is shown to be sufficient to provide a current density of 13mA/cm{sup 2} in the top cell. Finally, the influence of such thin top cells on the stabilized efficiency of the tandem cell is investigated by experiment and by means of semi-empirical modeling. Model and experiment confirm that such reduced-gap top cells, together with current enhancement due to the mirror layer, have a high potential for improving the stabilized efficiency of micromorph tandem cells.

  17. Method for determining transport critical current densities and flux penetration depth in bulk superconductors

    NASA Technical Reports Server (NTRS)

    Israelsson, Ulf E. (Inventor); Strayer, Donald M. (Inventor)

    1992-01-01

    A contact-less method for determining transport critical current density and flux penetration depth in bulk superconductor material. A compressor having a hollow interior and a plunger for selectively reducing the free space area for distribution of the magnetic flux therein are formed of superconductor material. Analytical relationships, based upon the critical state model, Maxwell's equations and geometrical relationships define transport critical current density and flux penetration depth in terms of the initial trapped magnetic flux density and the ratio between initial and final magnetic flux densities whereby data may be reliably determined by means of the simple test apparatus for evaluating the current density and flux penetration depth.

  18. Critical current density of domain wall oscillation due to spin-transfer torque

    NASA Astrophysics Data System (ADS)

    Taniguchi, T.; Imamura, H.

    2011-04-01

    The domain wall oscillation due to spin-transfer torque was studied by numerically solving the Landau-Lifshitz-Gilbert (LLG) equation. For a domain wall whose rotation angle θmax is less than 180°, we found the existence of the critical current density above which the magnetization dynamics are induced. We studied the dependence of the critical current density on the rotation angle θmax and found that the critical current density is proportional to 180° - θmax.

  19. Ironic Expression Can Simultaneously Enhance and Dilute Perception of Criticism

    ERIC Educational Resources Information Center

    Boylan, James; Katz, Albert N.

    2013-01-01

    In the context of texts that depicted either a minimally confrontational conversation (study 1) or a more confrontational argument (study 2) with a close friend, the use of ironic criticism was rated as being more humorous, polite, and positive, yet also as more sarcastic and mocking than direct criticism. Although our results were consistent with…

  20. Critical Thinking in Wikibook Creation with Enhanced and Minimal Scaffolds

    ERIC Educational Resources Information Center

    Kim, Nari

    2015-01-01

    The purpose of the study was to investigate how to scaffold students' critical thinking skills in the process of co-writing and co-reflection of wikibooks in formal learning contexts. To observe critical thinking skills in wiki collaborations under different levels of instructional guidance, two graduate wikibook projects were selected: an…

  1. Identifying Critical Thinking Styles to Enhance Volunteer Development

    ERIC Educational Resources Information Center

    Gay, Keegan D.; Terry, Bryan; Lamm, Alexa J.

    2015-01-01

    Diversity in learning options can increase efficacy of volunteer development systems. The University of Florida Critical Thinking Inventory (UFCTI) is designed to explicate an individual's critical thinking style based upon a continuum from Seeking Information to Engagement. Static and interpretive materials are best used with individuals of a…

  2. Apparatus and method for measuring critical current properties of a coated conductor

    DOEpatents

    Mueller, Fred M.; Haenisch, Jens

    2012-07-24

    The transverse critical-current uniformity in a superconducting tape was determined using a magnetic knife apparatus. A critical current I.sub.c distribution and transverse critical current density J.sub.c distribution in YBCO coated conductors was measured nondestructively with high resolution using a magnetic knife apparatus. The method utilizes the strong depression of J.sub.c in applied magnetic fields. A narrow region of low, including zero, magnetic field in a surrounding higher field is moved transversely across a sample of coated conductor. This reveals the critical current density distribution. A Fourier series inversion process was used to determine the transverse J.sub.c distribution in the sample.

  3. Relation of n-value to critical current in bent-damaged Bi2223 composite tape

    NASA Astrophysics Data System (ADS)

    Ochiai, S.; Okuda, H.; Sugano, M.; Hojo, M.; Osamura, K.; Kuroda, T.; Kumakura, H.; Kitaguchi, H.; Itoh, K.; Wada, H.

    The relation of n-value to critical current of bent-damaged (Bi,Pb)2Sr2Ca2Cu3O10+δ (Bi2223) composite tape was studied experimentally and analytically. The experimental results showed that, under bending strain, the n-value decreased rather slightly with decreasing critical current in comparison with the data obtained under applied tensile strain. The experimentally observed slight decrease in n-value with critical current under bending strain, and the measured changes in critical current and n-value with increasing bending strain, were described satisfactorily by the presented damage evolution model that correlates the extent of damage to variation of bending strain-induced tensile strain in the core along the thickness direction.

  4. Inflammatory Signals Enhance Piezo2-Mediated Mechanosensitive Currents

    PubMed Central

    Dubin, Adrienne E.; Schmidt, Manuela; Mathur, Jayanti; Petrus, Matthew J.; Xiao, Bailong; Coste, Bertrand; Patapoutian, Ardem

    2012-01-01

    Summary Heightened nociceptor function caused by inflammatory mediators such as bradykinin contributes to increased pain perception (hyperalgesia) to noxious mechanical and thermal stimuli. While sensitization of the heat transducer TRPV1 largely subserves thermal hyperalgesia, cellular mechanisms underlying mechanical hyperalgesia have been elusive. The role of the mechanically-activated (MA) channel piezo2 (known as FAM38B) present in mammalian sensory neurons is unknown. We test the hypothesis that piezo2 activity is enhanced by bradykinin, an algogenic peptide that induces mechanical hyperalgesia within minutes. Piezo2 current amplitude is increased and inactivation slowed by bradykinin 2 receptor (BDKRB2) activation in heterologous expression systems. Protein Kinase A (PKA) and Protein Kinase C (PKC) agonists enhance piezo2 activity. BDKRB2-mediated effects are abolished by PKA and PKC inhibitors. Finally, piezo2-dependent MA currents in a class of native sensory neurons are enhanced 8-fold by bradykinin via PKA and PKC. Thus, piezo2 sensitization may contribute to PKA- and PKC-mediated mechanical hyperalgesia. PMID:22921401

  5. Self-Magnetic Field Effects on Electron Emission as the Critical Current is Approached

    SciTech Connect

    Ottinger, P. F.; Cooperstein, G.; Schumer, J. W.; Swanekamp, S. B.

    2001-09-28

    The self-magnetic field associated with the current in a planar diode is shown to reduce electron emission below the Child-Langmuir current density. As the magnetic field increases, the diode current is limited to the critical current. Here, a ID analysis is carried out to calculate the suppressed current density in the presence of a transverse magnetic field. The problem is shown to be similar to that of the limiting current (i.e., Hull current) calculated in a crossed field gap, in which a constant transverse magnetic field is applied across the gap to insulate the electron flow. In the case considered here, the magnetic field is produced by the diode current itself and this self-magnetic field decreases with distance along the gap. It is shown that the emitted current density is only modestly reduced from the Child-Langmuir current density. The 1-D analysis remains valid until critical current is approached, at which point orbit crossing occurs and a 2-D kinetic analysis is required. The minimum diode length required to reach critical current is also derived.

  6. Substantial reduction of critical current for magnetization switching in an exchange-biased spin valve

    NASA Astrophysics Data System (ADS)

    Jiang, Y.; Nozaki, T.; Abe, S.; Ochiai, T.; Hirohata, A.; Tezuka, N.; Inomata, K.

    2004-06-01

    Great interest in current-induced magnetic excitation and switching in a magnetic nanopillar has been caused by the theoretical predictions of these phenomena. The concept of using a spin-polarized current to switch the magnetization orientation of a magnetic layer provides a possible way to realize future 'current-driven' devices: in such devices, direct switching of the magnetic memory bits would be produced by a local current application, instead of by a magnetic field generated by attached wires. Until now, all the reported work on current-induced magnetization switching has been concentrated on a simple ferromagnet/Cu/ferromagnet trilayer. Here we report the observation of current-induced magnetization switching in exchange-biased spin valves (ESPVs) at room temperature. The ESPVs clearly show current-induced magnetization switching behaviour under a sweeping direct current with a very high density. We show that insertion of a ruthenium layer between an ESPV nanopillar and the top electrode effectively decreases the critical current density from about 108 to 107 A cm-2. In a well-designed 'antisymmetric' ESPV structure, this critical current density can be further reduced to 2 × 106 A cm-2. We believe that the substantial reduction of critical current could make it possible for current-induced magnetization switching to be directly applied in spintronic devices, such as magnetic random-access memory.

  7. The Use of Argument Mapping to Enhance Critical Thinking Skills in Business Education

    ERIC Educational Resources Information Center

    Kunsch, David W.; Schnarr, Karin; van Tyle, Russell

    2014-01-01

    Complex business problems require enhanced critical thinking skills. In a dedicated, in-person critical thinking class, argument mapping techniques were used in conjunction with business and nonbusiness case studies to build the critical thinking skills of a group of master of business administration students. Results demonstrated that the…

  8. Magnetic Field Dependence of the Critical Current in S-N Bilayer Thin Films

    NASA Technical Reports Server (NTRS)

    Sadleir, John E.; Lee, Sang-Jun; Smith, Stephen James; Bandler, Simon; Chervenak, James; Kilbourne, Caroline A.; Finkbeiner, Fred M.; Porter, Frederick S.; Kelley, Richard L.; Adams, Joseph S.; Eckart, Megan E.; Busch, Sarah; Porst, Jan-Patrick

    2013-01-01

    Here we investigate the effects a non-uniform applied magnetic field has on superconducting transition-edge sensors (TESs) critical current. This has implications on TES optimization. It has been shown that TESs resistive transition can be altered by magnetic fields. We have observed critical current rectification effects and explained these effects in terms of a magnetic self-field arising from asymmetric current injection into the sensor. Our TES physical model shows that this magnetic self-field can result in significantly degraded or improved TES performance. In order for this magnetically tuned TES strategy to reach its full potential we are investigating the effect a non-uniform applied magnetic field has on the critical current.

  9. Critical current from dynamical boundary instability for fully frustrated Josephson junction arrays

    NASA Astrophysics Data System (ADS)

    Kim, Beom Jun; Minnhagen, Petter

    2000-03-01

    We investigate numerically the critical current of two-dimensional fully frustrated arrays of resistively shunted Josephson junctions at zero temperature. It is shown that a domino-type mechanism is responsible for the existence of a critical current lower than the one predicted from the translationally invariant flux lattice. This domino mechanism is demonstrated for uniform-current injection as well as for various busbar conditions. It is also found that inhomogeneities close to the contacts make it harder for the domino propagation to start, which increases the critical current towards the value based on the translational invariance. This domino-type vortex motion can be observed in experiments as voltage pulses propagating from the contacts through the array.

  10. Enhancing Working Memory Training with Transcranial Direct Current Stimulation.

    PubMed

    Au, Jacky; Katz, Benjamin; Buschkuehl, Martin; Bunarjo, Kimberly; Senger, Thea; Zabel, Chelsea; Jaeggi, Susanne M; Jonides, John

    2016-09-01

    Working memory (WM) is a fundamental cognitive ability that supports complex thought but is limited in capacity. Thus, WM training interventions have become very popular as a means of potentially improving WM-related skills. Another promising intervention that has gained increasing traction in recent years is transcranial direct current stimulation (tDCS), a noninvasive form of brain stimulation that can modulate cortical excitability and temporarily increase brain plasticity. As such, it has the potential to boost learning and enhance performance on cognitive tasks. This study assessed the efficacy of tDCS to supplement WM training. Sixty-two participants were randomized to receive either right prefrontal, left prefrontal, or sham stimulation with concurrent visuospatial WM training over the course of seven training sessions. Results showed that tDCS enhanced training performance, which was strikingly preserved several months after training completion. Furthermore, we observed stronger effects when tDCS was spaced over a weekend break relative to consecutive daily training, and we also demonstrated selective transfer in the right prefrontal group to nontrained tasks of visual and spatial WM. These findings shed light on how tDCS may be leveraged as a tool to enhance performance on WM-intensive learning tasks. PMID:27167403

  11. Current enhancement of CdTe-based solar cells

    SciTech Connect

    Paudel, Naba R.; Poplawsky, Jonathan D.; More, Karren Leslie; Yan, Yanfa

    2015-07-30

    We report on the realization of CdTe solar cell photocurrent enhancement using an n-type CdSe heterojunction partner sputtered on commercial SnO2/SnO2:F coated soda-lime glass substrates. With high-temperature close-space sublimation CdTe deposition followed by CdCl2 activation, this thin-film stack allows for substantial interdiffusion at the CdSe/CdTe interface facilitating a CdSexTe1-x alloy formation. The bowing effect causes a reduced optical bandgap of the alloyed absorber layer and, therefore, leads to current enhancement in the long-wavelength region and a decrease in open-circuit voltage (VOC). To overcome the VOC loss and maintain a high short-circuit current (JSC), the CdTe cell configuration has been modified using combined CdS:O/CdSe window layers. The new device structure has demonstrated enhanced collection from both short-and long-wavelength regions as well as a VOC improvement. With an optimized synthesis process, a small-area cell using CdS:O/CdSe window layer showed an efficiency of 15.2% with a VOC of 831 mV, a JSC of 26.3 mA/cm2, and a fill factor of 69.5%, measured under an AM1.5 illumination without antireflection coating. Furthermore, the results provide new directions for further improvement of CdTe-based solar cells.

  12. Current enhancement of CdTe-based solar cells

    DOE PAGESBeta

    Paudel, Naba R.; Poplawsky, Jonathan D.; More, Karren Leslie; Yan, Yanfa

    2015-07-30

    We report on the realization of CdTe solar cell photocurrent enhancement using an n-type CdSe heterojunction partner sputtered on commercial SnO2/SnO2:F coated soda-lime glass substrates. With high-temperature close-space sublimation CdTe deposition followed by CdCl2 activation, this thin-film stack allows for substantial interdiffusion at the CdSe/CdTe interface facilitating a CdSexTe1-x alloy formation. The bowing effect causes a reduced optical bandgap of the alloyed absorber layer and, therefore, leads to current enhancement in the long-wavelength region and a decrease in open-circuit voltage (VOC). To overcome the VOC loss and maintain a high short-circuit current (JSC), the CdTe cell configuration has been modifiedmore » using combined CdS:O/CdSe window layers. The new device structure has demonstrated enhanced collection from both short-and long-wavelength regions as well as a VOC improvement. With an optimized synthesis process, a small-area cell using CdS:O/CdSe window layer showed an efficiency of 15.2% with a VOC of 831 mV, a JSC of 26.3 mA/cm2, and a fill factor of 69.5%, measured under an AM1.5 illumination without antireflection coating. Furthermore, the results provide new directions for further improvement of CdTe-based solar cells.« less

  13. Critical Current Measurements of High phTc Superconducting Cuprate Nanostructures.

    NASA Astrophysics Data System (ADS)

    Morales, P.; Diciano, M.; Mok, M.; Perovic, D. D.; Wei, J. Y. T.; Ananth, V.; Skocpol, W.; Mohanty, P.

    2004-03-01

    High phTc superconducting nanostructures were fabricated using a chemical-free technique. Pulsed current measurements of the resistivity, current-voltage characteristics, and critical current density of the superconducting nanostructures show characteristic behaviour not present in measurements done in bulk and thin film samples. Possible correlations between the observed electrical transport behavior and mesoscopic domain structures, coulomb blockade, phase slip centres (PSC) and stripe domains will be discussed.

  14. Using Blogs to Enhance Critical Reflection and Community of Practice

    ERIC Educational Resources Information Center

    Yang, Shih-Hsien

    2009-01-01

    Using the theories of critical reflection and community of practice, the aim of this paper was to explore the use of blogs as a reflective platform in the training processes of English as a Foreign Language (EFL) student teachers, who were learning to teach English for future employment in Taiwan. They made use of blogs as a platform to critically…

  15. A self-consistent model for estimating the critical current of superconducting devices

    NASA Astrophysics Data System (ADS)

    Zermeño, V.; Sirois, F.; Takayasu, M.; Vojenciak, M.; Kario, A.; Grilli, F.

    2015-08-01

    Nowadays, there is growing interest in using superconducting wires or tapes for the design and manufacture of devices such as cables, coils, rotating machinery, transformers, and fault current limiters, among others. Their high current capacity has made them the candidates of choice for manufacturing compact and light cables and coils that can be used in the large-scale power applications described above. However, the performance of these cables and coils is limited by their critical current, which is determined by several factors, including the conductor’s material properties and the geometric layout of the device itself. In this work we present a self-consistent model for estimating the critical current of superconducting devices. This is of large importance when the operating conditions are such that the self-field produced by the current is a significant fraction of the total field. The model is based on the asymptotic limit when time approaches infinity of Faraday’s equation written in terms of the magnetic vector potential. It uses a continuous E-J relationship and takes the angular dependence of the critical current density on the magnetic flux density into account. The proposed model is used to estimate the critical current of superconducting devices such as cables, coils, and coils made of transposed cables with very high accuracy. The high computing speed of this model makes it an ideal candidate for design optimization.

  16. Subthreshold outward currents enhance temporal integration in auditory neurons.

    PubMed

    Svirskis, Gytis; Dodla, Ramana; Rinzel, John

    2003-11-01

    Many auditory neurons possess low-threshold potassium currents ( I(KLT)) that enhance their responsiveness to rapid and coincident inputs. We present recordings from gerbil medial superior olivary (MSO) neurons in vitro and modeling results that illustrate how I(KLT) improves the detection of brief signals, of weak signals in noise, and of the coincidence of signals (as needed for sound localization). We quantify the enhancing effect of I(KLT) on temporal processing with several measures: signal-to-noise ratio (SNR), reverse correlation or spike-triggered averaging of input currents, and interaural time difference (ITD) tuning curves. To characterize how I(KLT), which activates below spike threshold, influences a neuron's voltage rise toward threshold, i.e., how it filters the inputs, we focus first on the response to weak and noisy signals. Cells and models were stimulated with a computer-generated steady barrage of random inputs, mimicking weak synaptic conductance transients (the "noise"), together with a larger but still subthreshold postsynaptic conductance, EPSG (the "signal"). Reduction of I(KLT) decreased the SNR, mainly due to an increase in spontaneous firing (more "false positive"). The spike-triggered reverse correlation indicated that I(KLT) shortened the integration time for spike generation. I(KLT) also heightened the model's timing selectivity for coincidence detection of simulated binaural inputs. Further, ITD tuning is shifted in favor of a slope code rather than a place code by precise and rapid inhibition onto MSO cells (Brand et al. 2002). In several ways, low-threshold outward currents are seen to shape integration of weak and strong signals in auditory neurons. PMID:14669013

  17. Numerical Simulation of Critical Current Performance in Nb3Sn Strand Subjected to Periodic Bending Deformation

    NASA Astrophysics Data System (ADS)

    Murakami, Haruyuki; Ueda, Hiroshi; Ishiyama, Atsushi; Koizumi, Norikiyo; Okuno, Kiyoshi

    In the ITER Engineering Design Activity (EDA), four Nb3Sn model coils were developed and successfully tested. However, it was revealed that the critical current of the conductor degraded with the increase of electromagnetic force. One of the explanations of this phenomenon is a strand bending caused by enormous electromagnetic force. The authors therefore developed a simulation code using the distributed circuit model to investigate dependency of the critical current performance on the periodic bending deformation. The simulation results were in good agreement with the experiments. The dependence of the critical current on the periodic transverse load, temperature, periodic load pitch, thickness of Ta barrier which prevents Cu stabilizer to be contaminated by Sn, twist pitch of the strand and RRR of the bronze matrix was investigated using the developed code. The results showed that the critical current degraded less with decreasing the pitch of the transverse load and increasing the Ta barrier thickness. It suggests that the shorter cabling pitch and the larger bending stiffness prevent the critical current degradation.

  18. Control of voltage reversal in serially stacked microbial fuel cells through manipulating current: Significance of critical current density

    NASA Astrophysics Data System (ADS)

    An, Junyeong; Sim, Junyoung; Lee, Hyung-Sool

    2015-06-01

    Voltage reversal is a critical issue for serially stacking microbial fuel cells (MFCs). It occurs when current density in stacked MFCs increases over critical current density (jcritical). In this study, we clearly show that no voltage reversal occurs in stacked MFCs if current density is maintained below jcritical where the anode and the cathode potential in an inferior unit become identical, with an external resistance placed between individual MFCs. We define threshold resistance (Rthreshold) that enables current density below jcritical in stacked MFCs, and demonstrate the validity of Rthreshold theoretically and experimentally. Voltage reversal is controlled in the stacked MFC equipped with Rthreshold by which the current density in the stacked MFC is kept below jcritical. In comparison, a stacked MFC without Rthreshold faces voltage reversal over jcritical. Energy loss in Rthreshold is comparable to energy loss with other voltage control methods, such as passive or active methods. However, the Rthreshold approach is a simple, inexpensive way of controlling voltage reversal, especially for small MFCs (<50 mL).

  19. Enhanced plasma current collection from weakly conducting solar array blankets

    NASA Technical Reports Server (NTRS)

    Hillard, G. Barry

    1993-01-01

    Among the solar cell technologies to be tested in space as part of the Solar Array Module Plasma Interactions Experiment (SAMPIE) will be the Advanced Photovoltaic Solar Array (APSA). Several prototype twelve cell coupons were built for NASA using different blanket materials and mounting techniques. The first conforms to the baseline design for APSA which calls for the cells to be mounted on a carbon loaded Kapton blanket to control charging in GEO. When deployed, this design has a flexible blanket supported around the edges. A second coupon was built with the cells mounted on Kapton-H, which was in turn cemented to a solid aluminum substrate. A final coupon was identical to the latter but used germanium coated Kapton to control atomic oxygen attack in LEO. Ground testing of these coupons in a plasma chamber showed considerable differences in plasma current collection. The Kapton-H coupon demonstrated current collection consistent with exposed interconnects and some degree of cell snapover. The other two coupons experienced anomalously large collection currents. This behavior is believed to be a consequence of enhanced plasma sheaths supported by the weakly conducting carbon and germanium used in these coupons. The results reported here are the first experimental evidence that the use of such materials can result in power losses to high voltage space power systems.

  20. Enhanced plasma current collection from weakly conducting solar array blankets

    NASA Astrophysics Data System (ADS)

    Hillard, G. Barry

    1993-05-01

    Among the solar cell technologies to be tested in space as part of the Solar Array Module Plasma Interactions Experiment (SAMPIE) will be the Advanced Photovoltaic Solar Array (APSA). Several prototype twelve cell coupons were built for NASA using different blanket materials and mounting techniques. The first conforms to the baseline design for APSA which calls for the cells to be mounted on a carbon loaded Kapton blanket to control charging in GEO. When deployed, this design has a flexible blanket supported around the edges. A second coupon was built with the cells mounted on Kapton-H, which was in turn cemented to a solid aluminum substrate. A final coupon was identical to the latter but used germanium coated Kapton to control atomic oxygen attack in LEO. Ground testing of these coupons in a plasma chamber showed considerable differences in plasma current collection. The Kapton-H coupon demonstrated current collection consistent with exposed interconnects and some degree of cell snapover. The other two coupons experienced anomalously large collection currents. This behavior is believed to be a consequence of enhanced plasma sheaths supported by the weakly conducting carbon and germanium used in these coupons. The results reported here are the first experimental evidence that the use of such materials can result in power losses to high voltage space power systems.

  1. Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions

    NASA Astrophysics Data System (ADS)

    Rakyta, Péter; Kormányos, Andor; Cserti, József

    2016-06-01

    We study the Josephson current in long ballistic superconductor-monolayer graphene-superconductor junctions. As a first step, we have developed an efficient computational approach to calculate the Josephson current in tight-binding systems. This approach can be particularly useful in the long-junction limit, which has hitherto attracted less theoretical interest but has recently become experimentally relevant. We use this computational approach to study the dependence of the critical current on the junction geometry, doping level, and an applied perpendicular magnetic field B . In zero magnetic field we find a good qualitative agreement with the recent experiment of M. Ben Shalom et al. [Nat. Phys. 12, 318 (2016), 10.1038/nphys3592] for the length dependence of the critical current. For highly doped samples our numerical calculations show a broad agreement with the results of the quasiclassical formalism. In this case the critical current exhibits Fraunhofer-like oscillations as a function of B . However, for lower doping levels, where the cyclotron orbit becomes comparable to the characteristic geometrical length scales of the system, deviations from the results of the quasiclassical formalism appear. We argue that due to the exceptional tunability and long mean free path of graphene systems a new regime can be explored where geometrical and dynamical effects are equally important to understand the magnetic field dependence of the critical current.

  2. Critical Currents of MgB2 Wire and Tape in Magnetic Field under Bending Deformations

    NASA Astrophysics Data System (ADS)

    Abin, D. A.; Mineev, N. A.; Osipov, M. A.; Pokrovsky, S. V.; Rudnev, I. A.

    Nowadays MgB2 wires are attractive for designing real devices like motors and magnets. The latest production technologies allow to increase critical current value of wires. However, there is a problem of wire performance degradation under bending strain. Thus, there is a problem of manufacturing solenoids with small diameters, especially from ex situ MgB2 wires produced by powder-in-tube (PIT) technology. In this work, influence of bending on critical current Ic multifilament PIT ex situ MgB2 tape and wire has been studied. Critical current dependencies on external magnetic field Ic(H) were measured at liquid helium temperature in the range of fields from 2.5 T up to 8 T. Measurements were carried out in parallel (H||), and perpendicular (H⊥) orientation of external magnetic field to the sample surface. Voltage current characteristics (V-I) on tape samples were measured with bending on diameters D=30; 40; 60; 70; 80; 90;100 mm. It was shown that critical current density (Jc) decreases by 24% and by 28% for tape and wire respectively with decreasing bending diameter from 100 mm to 60 mm. It was found that the tape still had superconductive properties even with bending diameter D=30 mm, but its Jc decreased by 44% in comparison with Jc(D=100 mm). One more feature that was found is the appearance of resistive component in the voltage current characteristics for all bend diameters in magnetic fields H>3.5 T.

  3. Study of second generation, high-temperature superconducting coils: Determination of critical current

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Kim, Jae-Ho; Pamidi, Sastry; Chudy, Michal; Yuan, Weijia; Coombs, T. A.

    2012-04-01

    This paper presents the modeling of second generation (2 G) high-temperature superconducting (HTS) pancake coils using finite element method. The axial symmetric model can be used to calculate current and magnetic field distribution inside the coil. The anisotropic characteristics of 2 G tapes are included in the model by direct interpolation. The model is validated by comparing to experimental results. We use the model to study critical currents of 2 G coils and find that 100 μV/m is too high a criterion to determine long-term operating current of the coils, because the innermost turns of a coil will, due to the effect of local magnetic field, reach their critical current much earlier than outer turns. Our modeling shows that an average voltage criterion of 20 μV/m over the coil corresponds to the point at which the innermost turns' electric field exceeds 100 μV/m. So 20 μV/m is suggested to be the critical current criterion of the HTS coil. The influence of background field on the coil critical current is also studied in the paper.

  4. ['I'm worthless' and other forms of self-criticism: Current knowledge and therapeutic interventions].

    PubMed

    Maillard, Pauline; Kramer, Ueli

    2015-01-01

    Self-criticism is considered as a harsh or punitive evaluation of the self. It is omnipresent in culture, in daily life as well as in psychotherapy. Self-criticism can lead to question oneself but can also open new perspectives and guide us. However, it can become excessive, rigid, and might turn out to be deleterious. This present article focuses on the concept of self-criticism in clinical psychology and psychotherapy and aims to review current knowledge about this topic. First, its definition and the reasons for its development in individuals will be presented. Second, a description of the links between self-criticism and psychopathology will be made, in particular regarding depression. Finally, the third part of this article will be dedicated to the therapeutic interventions that can reduce self-criticism. PMID:26355490

  5. Critical Approaches to Accessibility for Technology-Enhanced Learning

    ERIC Educational Resources Information Center

    Lewthwaite, Sarah

    2011-01-01

    The term "accessibility" is broadly used to describe the degree to which a service or product gives learners the "ability to access" functionality, services or materials. In recent years there has been a push towards accessibility in technology-enhanced learning (TEL) across all levels of education. However, accessibility represents a shifting…

  6. Calibration of Hall sensor array for critical current measurement of YBCO tape with ferromagnetic substrate

    NASA Astrophysics Data System (ADS)

    Zhu, Yunpeng; Wang, Gang; Liu, Liyuan; Yang, Xinsheng; Zhao, Yong

    2015-12-01

    HAS (Hall sensor array) is a powerful tool to detect the uniformity of HTS (high temperature superconductor) tape through mapping the distribution of remanent or shielding field along the surface of the tape. However, measurement of HTS tape with ferromagnetic parts by HSA is still an issue because the ferromagnetic substrate has influence on the magnetic field around the HTS layer. In this work, a continuous HSA system has been designed to measure the critical current of the YBCO tape with ferromagnetic substrate. The relationship between the remanent field and critical current was calibrated by the finite element method. The result showed that the HSA is an effective method for evaluating the critical current of the HTS tape with ferromagnetic substrate.

  7. Critical current measurements of high Tc superconductors in a scanning low temperature cryostat

    SciTech Connect

    Telschow, K.L.; O'Brien, T.K.

    1991-01-01

    Maintaining uniformity of properties over long distances is one of the fabrication problems encountered with the new high {Tc} superconductors. Uniform properties are crucial in long tapes or wires with high critical current since local nonuniformities can limit the current carrying capacity of the whole piece. Transport critical currents in high {Tc} superconductors are conventionally measured with the contact 4-point probe DC current-voltage technique. This technique requires contact with the sample and and spatially averages over the region between the two voltage contacts. Two techniques have been used to infer the critical state model. The first uses the net magnetization of a suitably shaped sample in an external magnetic field. The second combines a DC magnetic field with AC induced currents to infer spatial flux profiles. The AC magnetization technique offers an advantage in that it is noncontacting; however, it also averages the measurement over a large area and requires that the sample be shaped and positioned such that it exhibits zero demagnetizing factor. This paper describes a measurement technique and a scanning cryostat assembly that are capable of determining local critical current in a tape or wire with high resolution and without any direct sample electrical contact. A small compensated coil was used to induce AC currents in slab-shaped samples. The coil was situated near the surface on one side of the slab. With this method, the AC probe can be used as a noncontacting dissipation probe, replacing the voltage probe in the 4-point contact method, when an externally driven transport current is used, or by itself as a local critical state generator and dissipation detector. The results are shown to be meaningful even when the internal magnetic field is not uniform due to shape demagnetizing effects. 10 refs., 5 figs.

  8. Mechanism for the peak effect of the critical current in superconducting multilayers

    SciTech Connect

    Takahashi, S.; Hirai, T.; Tachiki, M.

    1994-12-31

    The authors theoretically study the vortex states in superconducting multilayers whose components are superconductors with nearly same transition temperatures but very different upper critical fields. They solve the nonlinear ginzburg-Landau equations numerically for the vortex lattice state of the multilayers. Two kinds of different vortex lattice states appear between the lower and upper critical fields. From the free energy calculations, the authors determine the phase boundary between the two vortex lattice states and map a phase diagram in the H-T plane. The peak effect of the critical current observed in Nb/NbZr multilayers is discussed in connection with the vortex states in these multilayers.

  9. Critical current density and mechanism of vortex pinning in KxFe2-ySe₂ doped with S

    DOE PAGESBeta

    Lei, Hechang; Petrovic, C.

    2011-08-15

    We report the critical current density Jc in KxFe2-ySe2-zSz crystals. The Jc can be enhanced significantly with optimal S doping (z=0.99). For K0.70(7)Fe1.55(7)Se1.01(2)S0.99(2), the weak fishtail effect is found for H II c. The normalized vortex pinning forces follow the scaling law with a maximum position at 0.41 of the reduced magnetic field. These results demonstrate that the small size normal point defects dominate the vortex pinning mechanism.

  10. The influence of structural defects on intragranular critical currents of bulk MgB[sub 2].

    SciTech Connect

    Serquis, A.; Liao, Xiaozhou; Civale, L.; Zhu, Y. T.; Coulter, J. Y.; Peterson, D. E.; Mueller, F. M.

    2002-01-01

    Bulk MgB2 samples were prepared under different synthesis conditions and analyzed by scanning and transmission electron microscopy. The critical current densities were determined from the magnetization versus magnetic field curves of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow cooling process, the oxygen dissolved in bulk MgB2 at high synthesis temperatures can segregate and form nanometer-sized coherent precipitates of Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these precipitates act as effective flux pinning centers and therefore significantly improve the intra-grain critical current density and its field dependence.

  11. Critical current studies on fine filamentary NbTi accelerator wires

    SciTech Connect

    Garber, M.; Suenaga, M.; Sampson, W.B.; Sabatini, R.L.

    1985-01-01

    The magnets for the Superconductig Super Collider, a high energy proton colliding beam accelerator, require a superconductor with very high current density (>2400 A/mm/sup 2/ at 5 T) and very small filaments (approx. 2..mu..m in diameter). Previous work has shown that by controlling the formation of Cu/sub 4/Ti compound particles on the filament surfaces it is possible to make fine filamentary NbTi wire with high critical current density. The performance of multi-filamentary wire is characterized by the current density and the quantity ''n'' which describes the superconducting-normal transition. Micrographs of wires having high J/sub c/ and high n show smooth, uniform filaments. Recently wires of very high critical current and high n have been produced in experimental quantities by commercial manufactures.

  12. Thermally activated flux creep and critical current densities in high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Matsushita, Teruo

    The effect of flux creep is discussed for projected strongly pinned oxide superconductors. It is determined, that if a superconducting wire with a critical current density higher than 10-billion A/sq m at 77 K and 5 T can be produced, the wire will be able to be applied to equipment at high fields; nonzero critical density will be obtained even at 77 K and high fields. The decay of persistent current is expected to be noticeable even in such strongly pinned superconductors, when those are used at 77 K. Although this will be managed in power equipment by lowering the operating current; variation in the magnetic field due to the variation in the current distribution inside superconducting wires appears to be unavoidable. It is suggested that an effort should be made to reduce the variation by reducing the diameter of the superconducting filaments.

  13. A Critical Review of Digital Storyline-Enhanced Learning

    ERIC Educational Resources Information Center

    Novak, Elena

    2015-01-01

    Storyline is one of the major motivators that lead people to play video games. However, little empirical evidence exists on the instructional effectiveness of integrating a storyline into digital learning materials. This systematic literature review presents current empirical findings on the effects of a storyline game design element for human…

  14. Method of enhancing the upper critical field (HC sub 2 ) in high temperature superconducting ceramic copper oxide perovskites

    SciTech Connect

    Rosen, C.Z.

    1992-03-03

    This patent describes a method of increasing the current carrying capacity and enhancing the upper critical (H{sub c2}) in a Type II superconducting material. It comprises providing a sample of a Type II superconducting material; exposing the sample to gamma radiation ranging in dosage level from about ten million rads to about one hundred million rads at a dose rate of about three million rads per hour.

  15. Superconducting fluctuations in organic molecular metals enhanced by Mott criticality

    PubMed Central

    Nam, Moon-Sun; Mézière, Cécile; Batail, Patrick; Zorina, Leokadiya; Simonov, Sergey; Ardavan, Arzhang

    2013-01-01

    Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-Tc cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above Tc. By studying alloys of quasi-two-dimensional organic molecular metals in the κ-(BEDT-TTF)2X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all. PMID:24292063

  16. Fabrication of Bi-(Pb)-Sr-Ca-Cu-O mono- and multifilamentary superconductors and improvement in critical current density

    NASA Astrophysics Data System (ADS)

    Sekine, H.; Inoue, K.; Maeda, H.; Numata, K.

    1989-09-01

    This paper describes procedures for the fabrication of the Bi-(Pb)-Sr-Ca-Cu-O superconducting material as tapes without sheathing and as multifilamentary wires and tapes with Ag sheathing, together with results from metallurgical studies and measurements of superconducting properties. Tape specimens of 0.5-1.0-mm thickness, prepared by combination and repetition of cold work and sintering, showed critical current density Jc as high as 5000 A/sq cm at 77 K, with good reproducibility and reliability. A 1330-filament Bi-Pb-Sr-Ca-Cu-O wire with an Ag sheath showed critical temperature of about 105 K, and a multifilamentary tape specimen showed Jc of 1050 A/sq cm at 77 K. The process of repetition of cold work and sintering had the effect of Jc enhancement on multifilamentary tapes.

  17. Effects of grain size and grain boundary on critical current density of high T(sub c) superconducting oxides

    NASA Technical Reports Server (NTRS)

    Zhao, Y.; Zhang, Q. R.; Zhang, H.

    1990-01-01

    By means of adding impurity elements in high T sub c oxides, the effects were studied of grain size and grain boundary on the critical current density of the following systems: YBa2Cu3O(7-y) and Bi-Pr-Sr-Ca-Cu-O. In order to only change the microstructure instead of the superconductivity of the grains in the samples, the impurity elements were added into the systems in terms of the methods like this: (1) substituting Y with the lanthanide except Pr, Ce, and Tb in YBa2Cu3O(7-y) system to finning down grains in the samples, therefore, the effect can be investigated of the grain size on the critical current density of 1:2:3 compounds; (2) mixing the high T sub c oxides with the metal elements, such as Ag, according to the composition of (high T sub c oxide)1-xAgx to metallize the grain boundaries in the samples, studying the effect of the electric conductivity of the grain boundaries on the critical current density; (3) adding SiO2, PbO2, and SnO2 into the high T sub c oxide to form impurity phases in the grain boundaries, trying to find out the effects of the impurity phases or metalloid grain boundaries on the critical current density of the high T sub c superconductors. The experimental results indicate that in the case of of the presence of the metalloid grain boundaries finning down grains fails to enhance the j sub c, but restrains it strongly, the granular high T sub c superconductors with the small size grains coupled weakly is always the low j sub c system.

  18. Attachment insecurity, responses to critical incident distress, and current emotional symptoms in ambulance workers.

    PubMed

    Halpern, Janice; Maunder, Robert G; Schwartz, Brian; Gurevich, Maria

    2012-02-01

    Ambulance workers are exposed to critical incidents that may evoke intense distress and can result in long-term impairment. Individuals who can regulate distress may experience briefer post-incident distress and fewer long-term emotional difficulties. Attachment research has contributed to our understanding of individual differences in stress regulation, suggesting that secure attachment is associated with effective support-seeking and coping strategies, and fewer long-term difficulties. We tested the effect of attachment insecurity on emotional distress in ambulance workers, hypothesizing that (1) insecure attachment is associated with symptoms of current distress and (2) prolonged recovery from acute post-critical incident distress, coping strategies and supportive contact mediate this relationship. We measured (1) attachment insecurity, (2) acute distress, coping and social contact following an index critical incident and (3) current symptoms of post-traumatic stress, depression, somatization and burnout and tested the hypothesized associations. Fearful-avoidant insecure attachment was associated with all current symptoms, most strongly with depression (R=0.38, p<0.001). Fearful-avoidant attachment insecurity was also associated with maladaptive coping, reduced social support and slower recovery from social withdrawal and physical arousal following the critical incident, but these processes did not mediate the relationship between attachment insecurity and current symptoms. These findings are relevant for optimizing post-incident support for ambulance workers. PMID:22259158

  19. A Critical Analysis of Approaches To Targeted PTSD Prevention: Current Status and Theoretically Derived Future Directions

    ERIC Educational Resources Information Center

    Feldner, Matthew T.; Monson, Candice M.; Friedman, Matthew J.

    2007-01-01

    Although efforts to prevent posttraumatic stress disorder (PTSD) have met with relatively limited success, theoretically driven preventive approaches with promising efficacy are emerging. The current article critically reviews investigations of PTSD prevention programs that target persons at risk for being exposed to a traumatic event or who have…

  20. Purification of SoyScreen using critical carbon dioxide in a counter-current fractionation column

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This research evaluated the use of critical carbon dioxide (CO2) in a counter-current fractionation column for purifying SoyScreen, a mixture of feruloylated glycerides. The process concept was tested using a mixture consisting of triacylglycerides (TAGs), ethyl ferulate and fatty acid ethyl esters...

  1. Effect of Secondary Annealing Process on Critical Current Density in Highly Textured Bi-2212 Superconducting System

    NASA Astrophysics Data System (ADS)

    Aksan, M. A.; Madre, M. A.; Rasekh, Sh.; Constantinescu, G.; Torres, M. A.; Diez, J. C.; Sotelo, A.; Yakinci, M. E.

    2015-09-01

    Bi-2212 samples prepared by a solid-state reaction technique have been grown from the melt using the laser floating zone method. After annealing the as-grown bars, the samples showed a good grain alignment and a high transport critical current density. Secondary annealing processes were performed on the annealed samples with the aim of producing Bi-2212 phase controlled decomposition. Hence, the Bi-2201 phase and the secondary phases, which act as effective pinning centers, were obtained with the secondary annealing process. After these thermal treatments, the transport critical current densities of samples significantly increased, when compared to the annealed ones. The maximum critical current density was achieved when the samples were subjected to secondary annealing at 680°C for 168 h with an improvement of ~80%, compared to the annealed ones. Moreover, it was found that magnetization of the secondarily annealed samples was also increased. The magnetic critical current densities in these secondary annealed samples were about 3 times higher than the values obtained for the annealed ones. These results clearly indicate that the secondary annealing processes lead to the formation of effective pinning centers in the bulk material.

  2. Twin engineering for high critical current densities and twin boundary energy measurement in melt processed YBCO

    NASA Astrophysics Data System (ADS)

    Mei, Linfeng

    It has been proven that twin boundaries in YBa2Cu 3O7-delta (YBCO) are effective flux pinning centers. By increasing the twin density of a YBCO sample, it is possible to achieve a high critical current density (Jc). In this work, twin engineering for high critical current densities and strong flux pinning has been achieved in melt processed YBCO by increasing the annealing temperature up to 680°C. When the isothermal oxygenation temperature increases from 450°C to 680°C, the average twin boundary spacing of the samples decreases significantly, and its critical current density and flux pinning force are greatly increased. The prerequisites for twin boundary engineering for high critical current densities and strong flux pinning are also pointed out. For the first time, temperature dependent twin boundary energies (gammatw's) of melt processed YBCO are measured by the twin spacing method and the twin tip or shape method, and the geometrical factor alpha in the twin spacing method is estimated. As expected, the twin boundary energy of YBCO decreases with increasing temperature. In addition, the correlation between Jc and the concentrations of Y2BaCuO5 (211) and Samarium (Sm) in the melt-textured growth (MTG) YBCO has been studied, as well as the distributions of 211 and Sm in the MTG YBCO pellets. All our results can be applied towards microstructure tailoring for a high Jc and strong flux pinning in YBCO, especially in bulk YBCO samples.

  3. High critical current YBCO films prepared by an MOD process on RABiTS templates.

    SciTech Connect

    Li, X.; Rupich, M. W.; Kodenkandath, T.; Huang, Y.; Zhang, W.; Siegel, E.; Verebelyi, D. T.; Schoop, U.; Nguyen, N.; Thieme, C.; Chen, Z.; Feldman, D. M.; Larbalestier, D. C.; Holesinger, T. G.; Civale, L.; Jia, Q. X.; Maroni, A.; Rane, M. V.; Chemical Engineering; American Superconductor Corp.; Univ. of Wisconsin; LANL; State Univ. of New York

    2007-06-01

    The metal organic deposition (MOD) of YBCO high temperature superconducting films on RABiTS (rolling assisted biaxially textured substrates) templates has been developed at American Superconductor as a low-cost, scalable manufacturing process for the commercialization of the second generation (2G) HTS wire. The MOD process is based on the deposition of a triflu-oroacetate (TFA) based metal organic precursor film which is converted, in an ex-situ process, to the superconducting YBCO film. A major goal of the development has been achieving high critical currents. This paper reports the preparation and characterization of MOD-YBCO films with critical currents exceeding 500 A/cm-w (77 K, self-field) using a scaleable thick film approach on RABiTS templates. The high critical current films were obtained through optimization of the precursor composition, nucleation and growth conditions. The through-thickness dependence of the critical current density of MOD Alms as a function of film thickness and a correlation of the through-thickness transport properties and microstructure of the thick MOD/RABiTS samples is reported.

  4. AFM nano-plough planar YBCO micro-bridges: critical currents and magnetic field effects.

    PubMed

    Elkaseh, A A O; Perold, W J; Srinivasu, V V

    2010-10-01

    The critical current (Ic) of YBa2Cu3O7-x (YBCO) AFM plough micro-constrictions is measured as a function of temperature, width and the magnetic flux density (B), which was applied perpendicular to the YBCO ab-plane and surface of the bridges. C-axis oriented thin films of YBa2Cu3O7-x were deposited on MgO substrates using an inverted cylindrical magnetron (ICM) sputtering technique. The films were then patterned into 8-10 micron size strips, using standard photolithography and dry etching processes. Micro-bridges with widths between 1.9 microm to 4.1 microm were fabricated by using atomic force microscope (AFM) nanolithography techniques. Critical current versus temperature data shows a straight-line behavior, which is typical of constriction type Josephson junctions. The Ic versus B characteristics exhibited a modulation, and a suppression of the critical current of up to 84%. It was also found that the critical current increases with increasing constriction width. PMID:21137754

  5. Impact of biquadratic coupling on critical current density in Co/Cu/Ni-Fe nanopillar

    NASA Astrophysics Data System (ADS)

    Aravinthan, D.; Sabareesan, P.; Daniel, M.

    2016-05-01

    We have studied the effect of biquadratic coupling (BQC) on critical current density in the Co/Cu/Ni-Fe nanopillar by solving the magnetization switching dynamics of the free layer which is governed by Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. The LLGS equation is analytically solved for the time independent case and value of the critical current density required to initiate the magnetization switching is calculated. Its value in the absence of BQC is 0.8576×1012 Am-2 and in the presence of BQC its value increases to 1.0914×1012 Am-2. BQC field is acting along the easy axis which opposes the free layer magnetization moving to the out of plane and hence the value of critical current density is high in the presence of BQC. We can reduce the critical current density by reducing the BQC field which can be achieved by making the nanopillar with minimal or no roughness in the pinned and free layer.

  6. Marital Interaction and Marital Conflict: A Critical Evaluation of Current Research Strategies

    ERIC Educational Resources Information Center

    Glick, Bruce R.; Gross, Steven Jay

    1975-01-01

    Methods currently used to investigate interaction during marital conflict limit the validity and generalizability of findings concerning the determinants and consequences of couples' interaction styles. The respective advantages and limitations of two research strategies--questionnaires and simulation strategies--are critically evaluated. Several…

  7. Enhancing Critical Thinking, Writing and Disposition Preparedness amongst Four-Year University Teacher Education Students

    ERIC Educational Resources Information Center

    Lane-Patrice, Libra A.

    2013-01-01

    More and more, critical thinking and writing skills are necessary and of prime significance. Stakeholders across the board are concerned that students are deficient in these vital areas. The purpose of this study was to examine how the employment of specific, targeted and explicit critical thinking and writing instruction could enhance the…

  8. Effects of Active Learning on Enhancing Student Critical Thinking in an Undergraduate General Science Course

    ERIC Educational Resources Information Center

    Kim, Kyoungna; Sharma, Priya; Land, Susan M.; Furlong, Kevin P.

    2013-01-01

    To enhance students' critical thinking in an undergraduate general science course, we designed and implemented active learning modules by incorporating group-based learning with authentic tasks, scaffolding, and individual reports. This study examined the levels of critical thinking students exhibited in individual reports and the students'…

  9. Prescription privileges for psychologists: a comprehensive review and critical analysis of current issues and controversies.

    PubMed

    Lavoie, Kim L; Barone, Silvana

    2006-01-01

    The debate over whether clinical psychologists should be granted the right to prescribe psychoactive medications has received considerable attention over the past 2 decades in North America and, more recently, in the UK. Proponents of granting prescription privileges to clinical psychologists argue that mental healthcare services are in crisis and that the mental health needs of society are not being met. They attribute this crisis primarily to the inappropriate prescribing practices of general practitioners and a persistent shortage of psychiatrists. It is believed that, as they would increase the scope of the practice of psychology, prescription privileges for psychologists would enhance mental health services by increasing public access to qualified professionals who are able to prescribe. The profession of psychology remains divided on the issue, and opponents have been equally outspoken in their arguments. The purpose of the present article is to place the pursuit of prescription privileges for psychologists in context by discussing the historical antecedents and major forces driving the debate. The major arguments put forth for and against prescription privileges for psychologists are presented, followed by a critical analysis of the validity and coherence of those arguments. Through this analysis, the following question is addressed. Is there currently sufficient empirical support for the desirability, feasibility, safety and cost effectiveness of granting prescription privileges to psychologists? Although proponents of granting prescription privileges to psychologists present several compelling arguments in favour of this practice, there remains a consistent lack of empirical evidence for the desirability, feasibility, safety and cost effectiveness of this proposal. More research is needed before we can conclude that prescription privileges for psychologists are a safe and logical solution to the problems facing the mental healthcare system. PMID:16396524

  10. Nursing care plans versus concept maps in the enhancement of critical thinking skills in nursing students enrolled in a baccalaureate nursing program.

    PubMed

    Sinatra-Wilhelm, Tina

    2012-01-01

    Appropriate and effective critical thinking and problem solving is necessary for all nurses in order to make complex decisions that improve patient outcomes, safety, and quality of nursing care. With the current emphasis on quality improvement, critical thinking ability is a noteworthy concern within the nursing profession. An in-depth review of literature related to critical thinking was performed. The use of nursing care plans and concept mapping to improve critical thinking skills was among the recommendations identified. This study compares the use of nursing care plans and concept mapping as a teaching strategy for the enhancement of critical thinking skills in baccalaureate level nursing students. The California Critical Thinking Skills Test was used as a method of comparison and evaluation. Results indicate that concept mapping enhances critical thinking skills in baccalaureate nursing students. PMID:22856062

  11. Nonionic surfactants enhancing bactericidal activity at their critical micelle concentrations.

    PubMed

    Tobe, Seiichi; Majima, Toshiaki; Tadenuma, Hirohiko; Suekuni, Tomonari; Sakai, Kenichi; Sakai, Hideki; Abe, Masahiko

    2015-01-01

    Bactericidal activities of benzalkonium chloride [also known as alkyldimethylbenzylammonium chloride (ADBAC)] containing nonionic surfactants such as methyl ester ethoxylates (MEE) with the alkyl group C8-C14 and oxyethylene (EO) group of average adduct number 3-15 were measured against Escherichia coli and Staphylococcus aureus. Sample solutions containing MEE in the vicinity of the critical micelle concentration exhibited a dramatic decrease in viable bacterial counts. MEE with an alkyl group of C12 and an oxyethylene group of lower adduct number exhibited little viable bacterial counts than those having higher EO adduct numbers. MEE with reduced EO adduct numbers increased fluorescence intensity in E. coli using the viability stain SYTO 9. Our results show that MEE molecules with low EO adduct numbers exhibited bactericidal activity by increasing the permeability of the E. coli cell membrane. Sample solution containing ADBAC and MEE molecules with lower EO adduct numbers also displayed higher zeta potentials. Moreover, ADBAC molecules incorporated into micelles of MEE with lower EO adduct numbers were adsorbed onto the surface of E. coli, which augmented bactericidal activity. PMID:25492231

  12. Microstructure dependence of the c-axis critical current density in second-generation YBCO tapes.

    SciTech Connect

    Jia, Y.; Welp, U.; Crabtree, G. W.; Kwok, W. K.; Malozemoff, A. P.; Rupich, M. W.; Fleshler, S.; Clem, J. R.

    2011-10-01

    C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density J{sub c}{sup c} has been recently found to be orders of magnitude lower than the ab-plane critical current density J{sub c}{sup ab}. Here we report on J{sub c}{sup c} (77 K, sf) values of various YBa{sub 2}Cu{sub 3}O{sub 7}-based (YBCO) tapes with different microstructures. Our results show that the value of J{sub c}{sup c} (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy {gamma} = J{sub c}{sup ab}/J{sub c}{sup c} can reach values as high as 2070, implying that in the highest-anisotropy tape, {approx}20% of the tape width carries c-axis current in a helically wound power cable.

  13. Microstructure dependence of the c-axis critical current density in second generation YBCO tapes

    SciTech Connect

    Jia, Y. Welp, U. Crabtree, G.W.; Kwok, W.K.; Malozemoff, A.P.; Rupich, M.W.; Fleshler, S.; Clem, J.R.

    2011-10-31

    C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density J{sub c}{sup c} has been recently found to be orders of magnitude lower than the ab-plane critical current density J{sub c}{sup ab}. Here we report on J{sub c}{sup c} (77 K, sf) values of various YBa{sub 2}Cu{sub 3}O{sub 7}-based (YBCO) tapes with different microstructures. Our results show that the value of J{sub c}{sup c} (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy {gamma} = J{sub c}{sup ab}/J{sub c}{sup c} can reach values as high as 2070, implying that in the highest-anisotropy tape, {approx}20% of the tape width carries c-axis current in a helically wound power cable.

  14. Is faculty development critical to enhance teaching effectiveness?

    PubMed

    Bhatnagar, Kavita; Srivastava, Kalpana; Singh, Amarjit

    2010-07-01

    India has the highest number of medical colleges in the world and, consequently, the highest number of medical teachers. The unprecedented growth of medical institutions in India in the past two decades has led to a shortage of teachers and created a quality challenge for medical education. In recent years, though medical advances have been understood and adopted by many institutions, the same is not true for educational planning and implementation. There is a need for well-trained faculty who will help improve programs to produce quality graduates. The existing teachers' training programs are insufficient; both in number and aspects they cover, to meet this demand. Provision of faculty development related to teaching and assessment strategies is widely perceived to be the essential ingredient in the efforts to introduce new curricular approaches and modify the educational environment in academic medicine. Analyses of the outcomes of efforts to revise health professions curricula have identified the availability and effectiveness of faculty development as a predictor of the success or failure of reform initiatives. This article will address faculty development for the purpose of enhancing teaching effectiveness and preparing instructors for potential new roles associated with curriculum changes. PMID:22174541

  15. A Critical Appraisal of Solubility Enhancement Techniques of Polyphenols

    PubMed Central

    Kaur, Harkiran; Kaur, Gurpreet

    2014-01-01

    Polyphenols constitute a family of natural substances distributed widely in plant kingdom. These are produced as secondary metabolites by plants and so far 8000 representatives of this family have been identified. Recently, there is an increased interest in the polyphenols because of the evidence of their role in prevention of degenerative diseases such as neurodegenerative diseases, cancer, and cardiovascular diseases. Although a large number of drugs are available in the market for treatment of these diseases, however, the emphasis these days is on the exploitation of natural principles derived from plants. Most polyphenols show low in vivo bioavailability thus limiting their application for oral drug delivery. This low bioavailability could be associated with low aqueous solubility, first pass effect, metabolism in GIT, or irreversible binding to cellular DNA and proteins. Therefore, there is a need to devise strategies to improve oral bioavailability of polyphenols. Various approaches like nanosizing, self-microemulsifying drug delivery systems (SMEDDS), microencapsulation, complexation, and solid dispersion can be used to increase the bioavailability. This paper will highlight the various methods that have been employed till date for the solubility enhancement of various polyphenols so that a suitable drug delivery system can be formulated. PMID:26556188

  16. Is faculty development critical to enhance teaching effectiveness?

    PubMed Central

    Bhatnagar, Kavita; Srivastava, Kalpana; Singh, Amarjit

    2010-01-01

    India has the highest number of medical colleges in the world and, consequently, the highest number of medical teachers. The unprecedented growth of medical institutions in India in the past two decades has led to a shortage of teachers and created a quality challenge for medical education. In recent years, though medical advances have been understood and adopted by many institutions, the same is not true for educational planning and implementation. There is a need for well-trained faculty who will help improve programs to produce quality graduates. The existing teachers’ training programs are insufficient; both in number and aspects they cover, to meet this demand. Provision of faculty development related to teaching and assessment strategies is widely perceived to be the essential ingredient in the efforts to introduce new curricular approaches and modify the educational environment in academic medicine. Analyses of the outcomes of efforts to revise health professions curricula have identified the availability and effectiveness of faculty development as a predictor of the success or failure of reform initiatives. This article will address faculty development for the purpose of enhancing teaching effectiveness and preparing instructors for potential new roles associated with curriculum changes. PMID:22174541

  17. An exponential scaling law for the strain dependence of the Nb3Sn critical current density

    NASA Astrophysics Data System (ADS)

    Bordini, B.; Alknes, P.; Bottura, L.; Rossi, L.; Valentinis, D.

    2013-07-01

    The critical current density of the Nb3Sn superconductor is strongly dependent on the strain applied to the material. In order to investigate this dependence, it is a common practice to measure the critical current of Nb3Sn strands for different values of applied axial strain. In the literature, several models have been proposed to describe these experimental data in the reversible strain region. All these models are capable of fitting the measurement results in the strain region where data are collected, but tend to predict unphysical trends outside the range of data, and especially for large strain values. In this paper we present a model of a new strain function, together with the results obtained by applying the new scaling law on relevant datasets. The data analyzed consisted of the critical current measurements at 4.2 K that were carried out under applied axial strain at Durham University and the University of Geneva on different strand types. With respect to the previous models proposed, the new scaling function does not present problems at large strain values, has a lower number of fitting parameters (only two instead of three or four), and is very stable, so that, starting from few experimental points, it can estimate quite accurately the strand behavior in a strain region where there are no data. A relationship is shown between the proposed strain function and the elastic strain energy, and an analogy is drawn with the exponential form of the McMillan equation for the critical temperature.

  18. Comparison between the magnetic and transport critical current densities in high critical current density melt-textured yttrium barium copper-oxide

    NASA Technical Reports Server (NTRS)

    Gao, L.; Meng, R. L.; Xue, Y. Y.; Hor, P. H.; Chu, C. W.

    1991-01-01

    Using a recently developed pulsed critical current density (Jc) measuring system, the Jc of the high-Jc melt-textured YBa2Cu3O(7-delta) (Y123) bulk samples has been determined. I-V curves with a voltage resolution of 0.5 microV were obtained, and transport Jc's along the a-b plane as high as 7.2 x 10 to the 4th A/sq cm were extracted. These results are comparable to the values obtained magnetically. On the other hand, transport Jc along the c axis were found to be two orders of magnitude smaller, even though the magnetic Jc along the c axis is only about five times smaller than Jc along the a-b plane. It is suggested that for the high-temperature superconducting materials which are highly anisotropic, caution should be taken when using the nontransport magnetic methods to determine Jc.

  19. Critical currents of aligned grains of Tl-Ba-Ca-Cu-O compounds

    NASA Technical Reports Server (NTRS)

    Fang, M. M.; Finnemore, D. K.; Farrell, D. E.; Bansal, N. R.

    1989-01-01

    A study of irreversibility in the magnetization curves of Tl2Ba2Ca2Cu3O10 and Tl2Ba2Ca1Cu2O8 was undertaken to determine the intragranular critical currents and the effects of flux-creep in grain-aligned samples of these materials. For fields of greater than 0.3 T, and H parallel to c axis, the critical supercurrent falls approximately exponentially with both magnetic field and temperature. Flux-creep is found to be linear in the logarithm of time at low fields over a wide temperature range.

  20. Low field critical current density of titanium sheathed magnesium diboride wires

    NASA Astrophysics Data System (ADS)

    Rostila, L.; Grasso, G.; Demenčík, E.; Tumino, A.; Brisigotti, S.; Kováč, P.

    2010-06-01

    Magnesium diboride (MgB2) is replacing some of the conventional superconductors due to its low cost and availability in kilometer lengths. MgB2 has also been considered for AC applications. In order to model the AC losses and the critical currents of the applications, intrinsic Jc(B)-dependence is an important factor also at low fields. In this work Jc(B)-dependence of an MgB2 sample is extracted from the standard in field voltage-current measurements. The proposed method is applied to a non magnetic titanium sheathed sample at 16 and 20 K and a simple formula for Jc(B) aligns with the measurements. In the fitting process, the critical current distribution inside the wire is numerically simulated in order to take the self field of the sample into account. Moreover, the same formula aligns with measurements of a different sample. These critical current measurements, performed at 4.2 K, were based on magnetization. In the self field computations, the superconducting cross section must be determined accurately. Therefore, we tailored an image processing tool for MgB2 wires to obtain the geometry from a photograph.

  1. Upper critical field enhancements of TMB HPCVD magnesium diboride

    NASA Astrophysics Data System (ADS)

    Hunte, F.; Jaroszynski, J.; Gurevich, A.; Larbalestier, D. C.; Zhu, Y.; Voyles, P. M.; Wilke, R. H.; Xi, X. X.

    2008-03-01

    The Hc2 of four well textured carbon-doped MgB2 films grown by HPCVD from tri-methyl boron (TMB) at flow rates from 2.5 to 10 sccm was measured in fields up to 45T. Hc2 derived from low- current, four-point magnetoresistance clearly increases with increasing TMB flow rate. TMB appears to be a more uniform dopant than the (C6H7)2Mg used earlier. These earlier films exhibited Hc2^(0) up to 70 T but also were imperfectly connected (ρ(50 K)˜200-800 μφcm) due to excess amorphous C-rich phases observed between the MgB2 grains. In strong contrast, ρ(50 K) was only 10-20 μφcm for the TMB films. When first measured, the linearly extrapolated Hc2^(0) reached ˜40 T for the film with the highest TMB flow rate, but after about 3 months of aging, this value rose to ˜50 T. The angular dependence of Hc2 for this sample was measured up to 45 T yielding Hc2^(4.2 K) = 45.8 T and showing the good Ginzburg-Landau scaling with an Hc2 anisotropy of 2.88 at 4.2 K. These results are discussed in terms of the theory of dirty two-gap superconductors as a part of an in-depth study of the effect of ternary doping of magnesium diboride.

  2. Mechanism for the uniaxial strain dependence of the critical current in practical REBCO tapes

    NASA Astrophysics Data System (ADS)

    Osamura, Kozo; Machiya, Shutaro; Hampshire, Damian P.

    2016-06-01

    In order to elucidate the effect of uniaxial strain on the critical current of practical REBCO tapes (REBa2Cu3O7‑d , RE = Y and Gd) fabricated by Superpower and SuNAM, two types of critical current measurements were carried out. In the first, the tape sample was attached directly to a universal testing machine and pulled under a tensile load. In the second, the tape was soldered to a Cu–Be springboard and then attached to the testing machine and then pushed or pulled in order to apply both tensile and compressive strains to the tape sample. An inverse parabolic behaviour was observed for the uniaxial strain dependence of the critical current of both tapes. Using synchrotron radiation, the local strain exerted on the REBCO layer was measured at room temperature under the conditions used for the two techniques for making I c measurements. On the basis of these room temperature data, the local strain exerted on the REBCO layer at 77 K was numerically evaluated. A one-dimensional chain model for current flow in the REBCO material with fractional lengths of A-domains and B-domains oriented along the uniaxial strain direction is proposed. The model can explain the parabolic strain behaviour of the critical current and shows that the strain at which the peak in I c occurs, is not only determined by pre-compression or pre-tension on the superconductor at the operating temperature, but also by the ratio of the fractional amounts of the two domains.

  3. Critical Current Scaling in Long Diffusive Graphene-Based Josephson Junctions

    NASA Astrophysics Data System (ADS)

    Ke, Chung Ting; Borzenets, Ivan V.; Draelos, Anne W.; Amet, Francois; Bomze, Yuriy; Jones, Gareth; Craciun, Monica; Russo, Saverio; Yamamoto, Michihisa; Tarucha, Seigo; Finkelstein, Gleb

    2016-08-01

    We present transport measurements on long diffusive graphene-based Josephson junctions. Several junctions are made on a single-domain crystal of CVD graphene and feature the same contact width of ~9$\\mu$m but vary in length from 400 to 1000 nm. As the carrier density is tuned with the gate voltage, the critical current in the these junctions spans a range from a few nA up to more than $5\\mu$A, while the Thouless energy, ETh, covers almost two orders of magnitude. Over much of this range, the product of the critical current and the normal resistance IcRn is found to scale linearly with ETh, as expected from theory. However, the ratio IcRn /ETh is found to be 0.1-0.2: much smaller than the predicted ~10 for long diffusive SNS junctions.

  4. Critical current and instability threshold measurement of Nb3Sn cables for high field accelerator magnets

    SciTech Connect

    Ambrosio, G.; Andreev, N.; Bartlett, S.E.; Barzi, E.; Denarie, C.-H.; Dietderich, D.; Ghosh, A.K.; Verweij, A.P.; Zlobin, A.V.; /Fermilab

    2004-11-01

    Rutherford-type cables made of high critical current Nb{sub 3}Sn strands are being used in several laboratories for developing new generation superconducting magnets for present and future accelerators and upgrades. Testing of cable short samples is an important part of these R&D programs and the instability problem found in some short model magnets at Fermilab made these tests even more significant. Fermilab in collaboration with BNL, CERN and LBNL has developed sample holders and sample preparation infrastructure and procedures for testing Nb{sub 3}Sn cable short samples at BNL and CERN test facilities. This paper describes the sample holders, sample preparation and instrumentation, and test results. Several samples made of MJR or PIT strands 1 mm in diameter have been tested. Some samples were unstable (i.e. quenched at low transport currents) at low fields and reached the critical surface at higher fields.

  5. Critical Current Scaling in Long Diffusive Graphene-Based Josephson Junctions.

    PubMed

    Ke, Chung Ting; Borzenets, Ivan V; Draelos, Anne W; Amet, Francois; Bomze, Yuriy; Jones, Gareth; Craciun, Monica; Russo, Saverio; Yamamoto, Michihisa; Tarucha, Seigo; Finkelstein, Gleb

    2016-08-10

    We present transport measurements on long, diffusive, graphene-based Josephson junctions. Several junctions are made on a single-domain crystal of CVD graphene and feature the same contact width of ∼9 μm but vary in length from 400 to 1000 nm. As the carrier density is tuned with the gate voltage, the critical current in these junctions ranges from a few nanoamperes up to more than 5 μA, while the Thouless energy, ETh, covers almost 2 orders of magnitude. Over much of this range, the product of the critical current and the normal resistance ICRN is found to scale linearly with ETh, as expected from theory. However, the value of the ratio ICRN/ETh is found to be 0.1-0.2, which much smaller than the predicted ∼10 for long diffusive SNS junctions. PMID:27388297

  6. Critical-current diffraction patterns of grain-boundary Josephson weak links

    SciTech Connect

    Peterson, R.L.; Ekin, J.W. )

    1990-11-01

    We discuss the diffraction patterns and other characteristics of the critical current as a function of magnetic field in grain-boundary Josephson barriers. Diffraction patterns occur not just for {ital SIS} junctions but for all types of Josephson links, including {ital SNS} junctions, which may be present at grain boundaries in high-{Tc} superconductors. We discuss the generality of the Airy diffraction pattern, which is expected to characterize grain-boundary barriers in bulk material more accurately than the Fraunhofer pattern. The transport critical-current density in many bulk, granular high-{ital T}{sub {ital c}} superconductors has a power-law dependence on very low magnetic fields, characteristic of averaged diffraction patterns, and cannot be fitted by an exponential magnetic-field dependence, which may result from the material properties of the barriers.

  7. Critical carbon input to maintain current soil organic carbon stocks in global wheat systems.

    PubMed

    Wang, Guocheng; Luo, Zhongkui; Han, Pengfei; Chen, Huansheng; Xu, Jingjing

    2016-01-01

    Soil organic carbon (SOC) dynamics in croplands is a crucial component of global carbon (C) cycle. Depending on local environmental conditions and management practices, typical C input is generally required to reduce or reverse C loss in agricultural soils. No studies have quantified the critical C input for maintaining SOC at global scale with high resolution. Such information will provide a baseline map for assessing soil C dynamics under potential changes in management practices and climate, and thus enable development of management strategies to reduce C footprint from farm to regional scales. We used the soil C model RothC to simulate the critical C input rates needed to maintain existing soil C level at 0.1° × 0.1° resolution in global wheat systems. On average, the critical C input was estimated to be 2.0 Mg C ha(-1) yr(-1), with large spatial variability depending on local soil and climatic conditions. Higher C inputs are required in wheat system of central United States and western Europe, mainly due to the higher current soil C stocks present in these regions. The critical C input could be effectively estimated using a summary model driven by current SOC level, mean annual temperature, precipitation, and soil clay content. PMID:26759192

  8. Critical carbon input to maintain current soil organic carbon stocks in global wheat systems

    NASA Astrophysics Data System (ADS)

    Wang, Guocheng; Luo, Zhongkui; Han, Pengfei; Chen, Huansheng; Xu, Jingjing

    2016-01-01

    Soil organic carbon (SOC) dynamics in croplands is a crucial component of global carbon (C) cycle. Depending on local environmental conditions and management practices, typical C input is generally required to reduce or reverse C loss in agricultural soils. No studies have quantified the critical C input for maintaining SOC at global scale with high resolution. Such information will provide a baseline map for assessing soil C dynamics under potential changes in management practices and climate, and thus enable development of management strategies to reduce C footprint from farm to regional scales. We used the soil C model RothC to simulate the critical C input rates needed to maintain existing soil C level at 0.1° × 0.1° resolution in global wheat systems. On average, the critical C input was estimated to be 2.0 Mg C ha-1 yr-1, with large spatial variability depending on local soil and climatic conditions. Higher C inputs are required in wheat system of central United States and western Europe, mainly due to the higher current soil C stocks present in these regions. The critical C input could be effectively estimated using a summary model driven by current SOC level, mean annual temperature, precipitation, and soil clay content.

  9. Critical carbon input to maintain current soil organic carbon stocks in global wheat systems

    PubMed Central

    Wang, Guocheng; Luo, Zhongkui; Han, Pengfei; Chen, Huansheng; Xu, Jingjing

    2016-01-01

    Soil organic carbon (SOC) dynamics in croplands is a crucial component of global carbon (C) cycle. Depending on local environmental conditions and management practices, typical C input is generally required to reduce or reverse C loss in agricultural soils. No studies have quantified the critical C input for maintaining SOC at global scale with high resolution. Such information will provide a baseline map for assessing soil C dynamics under potential changes in management practices and climate, and thus enable development of management strategies to reduce C footprint from farm to regional scales. We used the soil C model RothC to simulate the critical C input rates needed to maintain existing soil C level at 0.1° × 0.1° resolution in global wheat systems. On average, the critical C input was estimated to be 2.0 Mg C ha−1 yr−1, with large spatial variability depending on local soil and climatic conditions. Higher C inputs are required in wheat system of central United States and western Europe, mainly due to the higher current soil C stocks present in these regions. The critical C input could be effectively estimated using a summary model driven by current SOC level, mean annual temperature, precipitation, and soil clay content. PMID:26759192

  10. C-axis critical current density of second-generation YBCO tapes.

    SciTech Connect

    Jia, Y.; Hua, J.; Crabtree, G. W.; Kwok, W. K.; Welp, U.; Malozemoff, A. P.; Rupich, M.; Fleshler, S.; Materials Science Division; American Superconductor Corp.

    2010-10-01

    We report on measurements of the temperature and field dependence of the c-axis critical current density (J{sub c}{sup c}) obtained on mesa structures that were patterned into the YBCO layer of second-generation HTS tapes. We find the J{sub c}{sup c}-values of {approx}4 kA cm{sup -2} at 77 K and self-field, corresponding to an unexpectedly high anisotropy in the critical current density J{sub c}{sup ab}/J{sub c}{sup c} of 500-600. C-axis current flow is expected to arise in applications such as the helically wound wires in HTS cables. A simple estimate is given of the fraction of tape width for such a c-axis flow; while in our samples this fraction is approximately 5% for a typical geometry, the fraction will grow linearly with increasing current density anisotropy and could affect the current-carrying ability of the tape.

  11. C-Axis critical current density of second-generation YBCO tapes

    SciTech Connect

    Jia, Y.; Hua, J.; Crabtree, G.W.; Kwok, W.K.; Welp, U.; Malozemoff, A.P.; Rupich, M.; Fleshler, S.

    2010-10-21

    We report on measurements of the temperature and field dependence of the c-axis critical current density (Jcc) obtained on mesa structures that were patterned into the YBCO layer of second-generation HTS tapes. We find the Jcc—values of ~ 4 kA cm-2 at 77 K and self-field, corresponding to an unexpectedly high anisotropy in the critical current density Jcab/Jcc of 500–600. C-axis current flow is expected to arise in applications such as the helically wound wires in HTS cables. A simple estimate is given of the fraction of tape width for such a c-axis flow; while in our samples this fraction is approximately 5% for a typical geometry, the fraction will grow linearly with increasing current density anisotropy and could affect the current-carrying ability of the tape.

  12. Josephson critical current of long SNS junctions in the presence of a magnetic field

    NASA Astrophysics Data System (ADS)

    Meier, Hendrik; Fal'Ko, Vladimir I.; Glazman, Leonid I.

    We evaluate the Josephson critical current of a long and wide two-dimensional superconductor-normal metal-superconductor (SNS) junction, taking into account the effect of electron reflection off the side edges of the junction. Considering clean junctions, we find that the effect of edges alters the usual Fraunhofer-like dependence of the Josephson critical current Ic on the magnetic flux Φ. At relatively weak fields, B <~Φ0 /W2 , the edge effect lifts zeros of the Ic (Φ) dependence and gradually shifts the maxima of that function by Φ0 / 2 . (Here W is the width of the junction and Φ0 the magnetic flux quantum.) At higher fields, B >~Φ0 /W2 , the edge effect leads to an accelerated decay of the critical current Ic (Φ) with increasing Φ. Our results are robust with respect to the roughness of realistic boundaries. Finally, we discuss the role of mesoscopic fluctuations of Ic (Φ) originating from the scattering off the edges, and compare our findings to recent experiments.

  13. Universal self-field critical current for thin-film superconductors

    PubMed Central

    Talantsev, E. F.; Tallon, J. L.

    2015-01-01

    For any practical superconductor the magnitude of the critical current density, Jc, is crucially important. It sets the upper limit for current in the conductor. Usually Jc falls rapidly with increasing external magnetic field, but even in zero external field the current flowing in the conductor generates a self-field that limits Jc. Here we show for thin films of thickness less than the London penetration depth, λ, this limiting Jc adopts a universal value for all superconductors—metals, oxides, cuprates, pnictides, borocarbides and heavy Fermions. For type-I superconductors, it is Hc/λ where Hc is the thermodynamic critical field. But surprisingly for type-II superconductors, we find the self-field Jc is Hc1/λ where Hc1 is the lower critical field. Jc is thus fundamentally determined and this provides a simple means to extract absolute values of λ(T) and, from its temperature dependence, the symmetry and magnitude of the superconducting gap. PMID:26240014

  14. Microwave Induced Enhancement of the Subgap Josephson dc Current

    NASA Astrophysics Data System (ADS)

    Lundin, N. I.; Shekhter, R. I.; Jonson, M.; Gorelik, L. Y.; Shumeiko, V. S.

    1998-03-01

    We introduce a mechanism for lifting the suppression of the subgap dc-Josephson current in a ballistic, normal, one-dimensional quantum channel between two superconducting electrodes with moderate amount of backscattering. The current appears when a non-equilibrium population of the Andreev levels carrying the current, is developed due to photon-induced Landua-Zener transitions.

  15. Finite temperature and density depletion effects on persistent current state transitions and critical velocity of a toroidal Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Kumar, Avinash; Eckel, Stephen; Jendrzejewski, Fred; Campbell, Gretchen

    We study the decay of a persistent, quantized current state in a toroidal geometry. Our experiment involves trapping neutral 23Na atoms in an all optical ``target trap'' shaped potential. This potential consists of a disc surrounded by an annular potential. A current in a superfluid can be sustained only below a critical current. This critical current can be tuned by introducing a density perturbation which depletes the local density. The decay time of a persistent current state can also be controlled by enhancing fluctuations of the system thermally. We study the decay at four different temperatures between 30 nK and 190 nK. For each temperature we record the decay at four different perturbation strengths. We find that increasing the magnitude of the density depletion or the temperature leads to a faster decay, and have seen the decay constant change by over two orders of magnitude. We also studied the size of hysteresis loop between different current states as a function of temperature, allowing us to extract a critical velocity. We find that the discrepancies between the experimentally extracted critical velocity and theoretically calculated critical velocity (using local-density approximation) decreases as the temperature is decreased. Now at University of Heidelberg.

  16. Ship waves on uniform shear current at finite depth: wave resistance and critical velocity

    NASA Astrophysics Data System (ADS)

    Li, Yan; Ellingsen, Simen Å.

    2016-03-01

    We present a comprehensive theory for linear gravity-driven ship waves in the presence of a shear current with uniform vorticity, including the effects of finite water depth. The wave resistance in the presence of shear current is calculated for the first time, containing in general a non-zero lateral component. While formally apparently a straightforward extension of existing deep water theory, the introduction of finite water depth is physically non-trivial, since the surface waves are now affected by a subtle interplay of the effects of the current and the sea bed. This becomes particularly pronounced when considering the phenomenon of critical velocity, the velocity at which transversely propagating waves become unable to keep up with the moving source. The phenomenon is well known for shallow water, and was recently shown to exist also in deep water in the presence of a shear current [Ellingsen, J.~Fluid Mech.\\ {\\bf 742} R2 (2014)]. We derive the exact criterion for criticality as a function of an intrinsic shear Froude number $S\\sqrt{b/g}$ ($S$ is uniform vorticity, $b$ size of source), the water depth, and the angle between the shear current and the ship's motion. Formulae for both the normal and lateral wave resistance force are derived, and we analyse its dependence on the source velocity (or Froude number $Fr$) for different amounts of shear and different directions of motion. The effect of the shear current is to increase wave resistance for upstream ship motion and decrease it for downstream motion. Also the value of $Fr$ at which $R$ is maximal is lowered for upstream and increased for downstream directions of ship motion. For oblique angles between ship motion and current there is a lateral wave resistance component which can amount to $10$-$20\\%$ of the normal wave resistance for side-on shear and $S\\sqrt{b/g}$ of order unity. (Continues...)

  17. Percolation thresholds in granular films—non-Universality and critical current

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, Scott

    1980-01-01

    The results are reported which should be applicable to the percolation threshold seen in the low temperature properties of inhomogeneous superconductors as the fraction of superconducting material is varied. First, we introduce a simplified model for the deposition of granular films, with an interaction enegy favoring the formation of metal clumps. The percolation problem defined on random samples prepared by this process is nonuniversal: critical exponents are continuous functions of the interaction strength and fiffer from the conventional values. Second, we treat the critical current, using the network model introduced recently by Deutscher and Rappaport[1], and by Huse and Guyer[2], neglecting the effects of structural correlation. Results are presented for 2D and 3D networks. In the course of these calculations, e have obtained a measure of the ''tortuousity'' of percolation paths close to threshold. Both results are conveniently expressed in terms of the percolation coherence length, ξp. The critical current density, Ic, is found to be ∝ξp1-d. The ratio of the network is ∝ in ξp in 2D and Ipδ/ν in 3D, with δ?.35.

  18. Hemodynamic Monitoring in the Critically Ill Patient – Current Status and Perspective

    PubMed Central

    Sakka, Samir G.

    2015-01-01

    In the critically ill patient, early and effective hemodynamic management including fluid therapy and administration of vasoactive drugs to maintain vital organ perfusion and oxygen delivery is mandatory. Understanding the different approaches in the management of critically ill patients during the resuscitation and further management is essential to initiate adequate context- and time-specific interventions. Treatment of hemodynamic variables to achieve a balance between organ oxygen delivery and consumption is the cornerstone. In general, cardiac output is considered a major determinant of oxygen supply and thus its monitoring is regarded helpful. However, indicators of oxygen requirements are equally necessary to assess adequacy of oxygen supply. Currently, more and more less or even totally non-invasive monitoring systems have been developed and clinically introduced, but require validation in this particular patient population. Cardiac output monitors and surrogates of organ oxygenation only enable to adequately guide management, as patient’s outcome is determined by acquisition and interpretation of accurate data, and finally suitable management decisions. This mini-review presents the currently available techniques in the field of hemodynamic monitoring in critically ill patients and briefly summarizes their advantages and limitations. PMID:26284244

  19. Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques

    SciTech Connect

    Lemery, F.; Mihalcea, D.; Prokop, C.R.; Piot, P.; /Northern Illinois U. /Fermilab

    2012-07-08

    In recent years, wakefield acceleration has gained attention due to its high acceleration gradients and cost effectiveness. In beam-driven wakefield acceleration, a critical parameter to optimize is the transformer ratio. It has been shown that current shaping of electron beams allows for enhanced (> 2) transformer ratios. In this paper we present the optimization of the pulse shape of the drive bunch for dielectric-wakefield acceleration.

  20. Induced convective enhancement of the critical heat flux from partially heated horizontal flat plates in saturated pool boiling

    SciTech Connect

    Bockwoldt, T.S.; Jeter, S.M.; Abdel-Khalik, S.I.; Hartley, J.G. )

    1992-05-01

    Current developments in high-power electronics and other energy-intensive applications have accentuated the need for higher performance heat transfer. Nucleate boiling heat transfer is one of the most effective modes of heat transfer, with pool boiling being perhaps the simplest type of passive two-phase cooling. Unfortunately, the maximum heat flux attainable in nucleate pool boiling is limited by the relatively low critical heat flux at the onset of film boiling. Several methods have been suggested to enhance the critical heat flux. In particular, Costello et al. showed that the critical heat flux in saturated pool boiling could be enhanced by simply increasing the width of the pool while maintaining a fixed heater size. Elkassabgi and Lienhard examined the combined effects of immersion depth and pool size on the critical heat flux for a small-diameter horizontal cylinder in saturated pool boiling. No similar study for flat plate heaters appears in the literature. While as noted above the effect of heater appears in the literature. While as noted above the effect of heater appears in the literature. While as noted above the effect of heater size and immersion depth have been studied independently, no systematic investigation of the combined effects has been conducted previously. This paper presents the results of such a study.

  1. Critical currents of YBCO tapes and Bi-2212 wires at different temperatures and magnetic fields

    SciTech Connect

    Lombardo, V.; Barzi, e.; Turrioni, D.; Zlobin, A.V.; /Fermilab

    2010-08-01

    Design studies for the cooling channel of a Muon Collider call for straight and helical solenoids generating field well in excess of the critical fields of state of the art Low Temperature Superconductors (LTS) such as Nb{sub 3}Sn or NbTi. Therefore, High Temperature Superconductors (HTS) will need to be used for the manufacturing of all or certain sections of such magnets to be able to generate and withstand the field levels at the cryogenic temperatures required by the new machine. In this work, two major High Temperature Superconductors - Bi2212 round wires and YBCO coated conductor tapes - are investigated to understand how critical current density of such conductors scales as a function of external field and operating temperature. This is vital information to make conductor choices depending on the application and to proceed with the design of such magnets.

  2. Concerning factors which determine whether flux-lattice shear or pin breaking limits the critical current density of superconductors

    SciTech Connect

    Welch, D.O.

    1992-10-01

    An elementary model is presented which illustrates the conditions under which flux-lattice shear, rather than pin breaking, limits the critical current density. An expression for the shear strength of the flux-lattice, based on the plasticity of metals and alloys, is used to derive the critical current density, including the effect of thermal activation in the flux creep regime.

  3. Concerning factors which determine whether flux-lattice shear or pin breaking limits the critical current density of superconductors

    SciTech Connect

    Welch, D.O.

    1992-01-01

    An elementary model is presented which illustrates the conditions under which flux-lattice shear, rather than pin breaking, limits the critical current density. An expression for the shear strength of the flux-lattice, based on the plasticity of metals and alloys, is used to derive the critical current density, including the effect of thermal activation in the flux creep regime.

  4. Defect enhanced funneling of diffusion current in silicon

    NASA Astrophysics Data System (ADS)

    Azimi, S.; Dang, Z. Y.; Song, J.; Breese, M. B. H.; Vittone, E.; Forneris, J.

    2013-01-01

    We report a current transport mechanism observed during electrochemical anodization of ion irradiated p-type silicon, in which a hole diffusion current is highly funneled along the gradient of modified doping profile towards the maximum ion induced defect density, dominating the total current flowing and hence the anodization behaviour. This study is characterized within the context of electrochemical anodization but relevant to other fields where any residual defect density may result in similar effects, which may adversely affect performance, such as in wafer gettering or satellite-based microelectronics. Increased photoluminescence intensity from localized buried regions of porous silicon is also shown.

  5. A Monte Carlo simulation on critical current distribution of bent-damaged multifilamentary Bi2223 composite tape

    NASA Astrophysics Data System (ADS)

    Ochiai, S.; Okuda, H.; Fujimoto, M.; Shin, J. K.; Oh, S. S.; Ha, D. W.

    2011-11-01

    It was attempted to reproduce the measured critical current ( I c) distributions of the Bi2223 composite tape bent by 0-0.833% by simulation. Simulation was carried out with a Monte Carlo method in combination with a model that correlates the critical current to damage evolution. Two variables that differ from specimen to specimen were input in the simulation. One was the damage strain parameter, with which the difference in extent of damage among specimens was expressed. Another was the original critical current ( I c0) values at zero bending strain. With the present simulation approach, the measured distributions of critical current at various bending strains, and the measured variations of average and coefficient of variation of critical current values with increasing bending strain were reproduced well.

  6. Workplace Learning Curriculum Guides. Volume VII: Enhanced Basic Skills--Decisions, Teams, Problem Solving, Critical Thinking.

    ERIC Educational Resources Information Center

    Colorado Community Coll. and Occupational Education System, Denver.

    This volume, one of a series of curriculum guides compiled by the Colorado Workplace Learning Initiative: 1991-92, contains seven workplace literacy courses on enhanced basic skills involving decisions, teams, problem solving, and critical thinking. Introductory materials include a table of contents and a list of the curriculum topics covered by…

  7. Values Advocacy: Enhancing Organizational Images, Deflecting Public Criticism, and Grounding Future Arguments.

    ERIC Educational Resources Information Center

    Bostdorff, Denise M.; Vibbert, Steven L.

    1994-01-01

    Argues that organizations routinely engage in values advocacy (the appeal to shared cultural values) to perform three distinct functions: (1) to enhance the organization's image; (2) to deflect criticism of the organization and/or its policies, products, and services; and (3) to establish value premises that can be used in later discourse. (SR)

  8. Enhancing Critical Reflection and Writing Skills in the HBSE Classroom and beyond

    ERIC Educational Resources Information Center

    Wiener, Diane R.

    2012-01-01

    Human Behavior in the Social Environment (HBSE) is an ideal location in which graduate social work students can enhance their critical reflection and writing skills while integrating social work theories with practice, research, and policy. A writing-intensive, learner-centered model using specific strategies is described via a framework of…

  9. The Case Study Method: Critical Thinking Enhanced by Effective Teacher Questioning Skills.

    ERIC Educational Resources Information Center

    Wood, Alexander T.; Anderson, Carol H.

    A diverse body of educational research provides strong theoretical support for the development of higher order cognitive learning skills through case teaching. Case study teachers can improve their questioning skills to enhance students' critical thinking. The theoretical background for questioning in case method teaching and learning is traceable…

  10. Enhancing Undergraduate Critical Reading Skills in Neuroscience Using Instructor-Developed Study Guides

    ERIC Educational Resources Information Center

    Moraru, Andreea; LeBoutillier, Janelle C.

    2009-01-01

    This study proposes an innovative instructional method for enhancing critical reading skills. Students enrolled in an undergraduate neuroscience course offered at the University of Toronto Scarborough reported that they often experience difficulty in analyzing and interpreting empirical and review journal articles. Our research focuses on student…

  11. Method and composition for improving flux pinning and critical current in superconductors

    DOEpatents

    Morris, D.E.

    1995-07-04

    Superconducting materials and methods of forming superconducting materials are disclosed. Highly oxidized superconductors are heated at a relatively high temperature so as to release oxygen, which migrates out of the material, and form a non-superconducting phase which does not diffuse out of grains of the material. The material is then reoxidized at a lower temperature, leaving the non-superconducting inclusions inside a superconducting phase. The non-superconducting inclusions act as pinning centers in the superconductor, increasing the critical current thereof. 14 figs.

  12. Influence of Indentation on the Critical Current of Nb3Sn Strands

    NASA Astrophysics Data System (ADS)

    Tomone, Suwa; Yoshihiro, Nabara; Yoshikazu, Takahashi; Masayuki, Oshikiri; Fumiaki, Tsutsumi; Kazuyuki, Shibutani; Yoshihiko, Nunoya; Yukinobu, Murakami; Katsumi, Miyashita; Sim, Ki-Hong; Kwon, Soun Pil

    The Japan Atomic Energy Agency (JAEA) is procuring Central Solenoid (CS) conductorsfor all modules forITER. The superconducting properties of the Nb3Sn CS conductors will have to sustain 60,000 electromagnetic (EM) cycles. The current sharing temperatures (Tcs) were stable with EM cycles in short twist pitch conductors.However, the short twist pitch and tight cabling increases indented strands at the contact point between strands before heat treatment. The results of Ic measurement on artificially indented Nb3Sn strands indicate that Ic was almost constant within a critical depth of the indentations.

  13. The critical current density in the layered superconductors with ferromagnetic nanorods

    NASA Astrophysics Data System (ADS)

    Kashurnikov, V. A.; Maksimova, A. N.; Rudnev, I. A.; Odintsov, D. S.

    2016-09-01

    In this paper, we have calculated the dependence of critical current density jc on the radius R and concentration of extended ferromagnetic defects in the system simulating a high-temperature superconductor (HTSC) layer. It was shown that at fixed volume concentration of ferromagnetic fraction the jc (R) dependence, as against nonmagnetic defects, has one maximum or two maxima at certain magnetization values of ferromagnetic fraction. We found that these maxima are due to the interplay of two parameters: concentration and effective depth of potential wells of defects.

  14. Critical field enhancement of asymptotic optical bound states in the continuum

    PubMed Central

    Yoon, Jae Woong; Song, Seok Ho; Magnusson, Robert

    2015-01-01

    We study spectral singularities and critical field enhancement factors associated with embedded photonic bound states in subwavelength periodic Si films. Ultrahigh-Q resonances supporting field enhancement factor exceeding 108 are obtained in the spectral vicinity of exact embedded eigenvalues in spite of deep surface modulation and vertical asymmetry of the given structure. Treating relations between the partial resonance Q and field enhancement factors with an analytical coupled-mode model, we derive a general strategy to maximize the field enhancement associated with these photonic bound states in the presence of material dissipation. The analytical expression for the field enhancement quantitatively agrees with rigorous numerical calculations. Therefore, our results provide a general knowledge for designing practical resonance elements based on optical bound states in the continuum in various applications. PMID:26673548

  15. Critical field enhancement of asymptotic optical bound states in the continuum.

    PubMed

    Yoon, Jae Woong; Song, Seok Ho; Magnusson, Robert

    2015-01-01

    We study spectral singularities and critical field enhancement factors associated with embedded photonic bound states in subwavelength periodic Si films. Ultrahigh-Q resonances supporting field enhancement factor exceeding 10(8) are obtained in the spectral vicinity of exact embedded eigenvalues in spite of deep surface modulation and vertical asymmetry of the given structure. Treating relations between the partial resonance Q and field enhancement factors with an analytical coupled-mode model, we derive a general strategy to maximize the field enhancement associated with these photonic bound states in the presence of material dissipation. The analytical expression for the field enhancement quantitatively agrees with rigorous numerical calculations. Therefore, our results provide a general knowledge for designing practical resonance elements based on optical bound states in the continuum in various applications. PMID:26673548

  16. Critical field enhancement of asymptotic optical bound states in the continuum

    NASA Astrophysics Data System (ADS)

    Yoon, Jae Woong; Song, Seok Ho; Magnusson, Robert

    2015-12-01

    We study spectral singularities and critical field enhancement factors associated with embedded photonic bound states in subwavelength periodic Si films. Ultrahigh-Q resonances supporting field enhancement factor exceeding 108 are obtained in the spectral vicinity of exact embedded eigenvalues in spite of deep surface modulation and vertical asymmetry of the given structure. Treating relations between the partial resonance Q and field enhancement factors with an analytical coupled-mode model, we derive a general strategy to maximize the field enhancement associated with these photonic bound states in the presence of material dissipation. The analytical expression for the field enhancement quantitatively agrees with rigorous numerical calculations. Therefore, our results provide a general knowledge for designing practical resonance elements based on optical bound states in the continuum in various applications.

  17. Pb/InAs nanowire josephson junction with high critical current and magnetic flux focusing.

    PubMed

    Paajaste, J; Amado, M; Roddaro, S; Bergeret, F S; Ercolani, D; Sorba, L; Giazotto, F

    2015-03-11

    We have studied mesoscopic Josephson junctions formed by highly n-doped InAs nanowires and superconducting Ti/Pb source and drain leads. The current-voltage properties of the system are investigated by varying temperature and external out-of-plane magnetic field. Superconductivity in the Pb electrodes persists up to ∼7 K and with magnetic field values up to 0.4 T. Josephson coupling at zero backgate voltage is observed up to 4.5 K and the critical current is measured to be as high as 615 nA. The supercurrent suppression as a function of the magnetic field reveals a diffraction pattern that is explained by a strong magnetic flux focusing provided by the superconducting electrodes forming the junction. PMID:25671540

  18. Current status of A1 adenosine receptor allosteric enhancers.

    PubMed

    Romagnoli, Romeo; Baraldi, Pier Giovanni; Moorman, Allan R; Borea, Pier Andrea; Varani, Katia

    2015-01-01

    Adenosine is an ubiquitous nucleoside involved in various physiological and pathological functions by stimulating A1, A2A, A2B and A3 adenosine receptors (ARs). Allosteric enhancers to A1ARs may represent novel therapeutic agents because they increase the activity of these receptors by mediating a shift to their active form in the A1AR-G protein ternary complex. In this manner, they are able to amplify the action of endogenous adenosine, which is produced in high concentrations under conditions of metabolic stress. A1AR allosteric enhancers could be used as a justifiable alternative to the exogenous agonists that are characterized by receptor desensitization and downregulation. In this review, an analysis of some of the most interesting allosteric modulators of A1ARs has been reported. PMID:26144263

  19. Enhanced Eddy-Current Detection Of Weld Flaws

    NASA Technical Reports Server (NTRS)

    Van Wyk, Lisa M.; Willenberg, James D.

    1992-01-01

    Mixing of impedances measured at different frequencies reduces noise and helps reveal flaws. In new method, one excites eddy-current probe simultaneously at two different frequencies; usually, one of which integral multiple of other. Resistive and reactive components of impedance of eddy-current probe measured at two frequencies, mixed in computer, and displayed in real time on video terminal of computer. Mixing of measurements obtained at two different frequencies often "cleans up" displayed signal in situations in which band-pass filtering alone cannot: mixing removes most noise, and displayed signal resolves flaws well.

  20. Analysis of the anisotropic critical current behaviour of HTS coated conductors

    NASA Astrophysics Data System (ADS)

    Leys, P. M.; Klaeser, M.; Schleissinger, F.; Schneider, Th

    2014-05-01

    In order to generate fields of more than 20 T using pure superconducting magnets, the implementation of HTS coated conductors (CCs) is an option. Amongst the characteristics of the REBCO is its intrinsic anisotropy which means its critical current, Ic, varies as a function of its orientation with respect to the external magnetic field, phi, as well as being dependent on external field, B, and temperature, T. For the design of the high field insert coils for the experimental magnet facility HOMER II, the behaviour of Ic at fields of about 24 T and at phi approximately 80 ° is required. Within our JUMBO facility it is possible to measure the U(I) behaviour of commercial CCs at liquid helium and liquid nitrogen temperatures. The free bore available is 100 mm at 4.2 K; the applied magnetic field can be varied up to 10 T, and phi can be set between 0 and 180 °. Measurements were carried out on commercially available CCs with emphasis on phi values near to 90 °. The critical current was determined by means of a power law function fitted to the resulting U(I) curves using specially written Matlab® programs. A number of different three dimensional functions were fitted to the measurement data and compared with each other.

  1. Magnetization and critical currents of tin-core multifilamentary Nb sub 3 Sn conductors

    SciTech Connect

    Ghosh, A.K.; Suenaga, M.

    1990-01-01

    This paper presents critical current and magnetization data for some multifilamentary Nb{sub 3}Sn wires that have been produced by the internal-tin method. A comparison of magnetization and transport critical current measurements show that filament bridging during heat treatment is a common occurrence leading to effective filament diameters that are sometimes an order of magnitude larger than the geometrical filament size. At present, J{sub c}'s (in the non-copper region) greater than 1300 A/mm{sup 2} at 10T have been achieved in some conductors, which also exhibit high losses. Low losses have only been seen in conductors with a high local ratio of niobium to copper. Also the use of (Nb-1%Ti) alloy instead of pure Nb helps to reduce low field loss and increase high field J{sub c}. Measurements of the temperature dependence of hysteretic loss to 5T indicate that loss decreases linearly with increasing temperature. 22 refs., 6 figs., 2 tabs.

  2. Self-field effects upon the critical current density of flat superconducting strips

    NASA Astrophysics Data System (ADS)

    Babaei Brojeny, Ali A.; Clem, John R.

    2005-06-01

    We develop a general theory to account self-consistently for self-field effects upon the average transport critical current density Jc of a flat type-II superconducting strip in the mixed state when the bulk pinning is characterized by a field-dependent depinning critical current density Jp(B), where B is the local magnetic flux density. We first consider the possibility of both bulk and edge-pinning contributions but conclude that bulk pinning dominates over geometrical edge-barrier effects in state-of-the-art YBCO films and prototype second-generation coated conductors. We apply our theory using the Kim model, JpK(B) = JpK(0)/(1+|B|/B0), as an example. We calculate Jc(Ba) as a function of a perpendicular applied magnetic induction Ba and show how Jc(Ba) is related to JpK(B). We find that Jc(Ba) is very nearly equal to JpK(Ba) when Ba>=Ba*, where Ba* is the value of Ba that makes the net flux density zero at the strip's edge. However, Jc(Ba) is suppressed relative to JpK(Ba) at low fields when Ba< Ba*, with the largest suppression occurring when Ba*/B0 is of order unity or larger.

  3. High critical currents in heavily doped (Gd,Y)Ba2Cu3Ox superconductor tapes

    DOE PAGESBeta

    Selvamanickam, V.; Gharahcheshmeh, M. Heydari; Xu, A.; Galstyan, E.; Delgado, L.; Cantoni, C.

    2015-01-20

    REBa2Cu3Ox superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50 K and fields of 2–30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (Jc) above 20 MA/cm2 at 30 K, 3 T in heavily doped (25 mol. % Zr-added) (Gd,Y)Ba2Cu3Ox superconductor tapes, which is more than three times higher thanmore » the Jc typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m3 have also been attained at 20 K. A composition map of lift factor in Jc (ratio of Jc at 30 K, 3 T to the Jc at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO3 (BZO) nanocolumn defect density of nearly 7 × 1011 cm–2 as well as 2–3nm sized particles rich in Cu and Zr have been found in the high Jc films.« less

  4. Electroencephalographic Monitoring in Critically Ill Children: Current Practice and Implications for Future Study Design

    PubMed Central

    Sánchez, Sarah M; Arndt, Daniel H.; Carpenter, Jessica L.; Chapman, Kevin E; Cornett, Karen M.; Dlugos, Dennis J.; Gallentine, William B.; Giza, Christopher C; Goldstein, Joshua L; Hahn, Cecil D; Lerner, Jason T; Loddenkemper, Tobias; Matsumoto, Joyce H; McBain, Kristin; Nash, Kendall B; Payne, Eric; Sánchez Fernández, Iván; Shults, Justine; Williams, Korwyn; Yang, Amy; Abend, Nicholas S.

    2014-01-01

    Purpose Survey data indicate that continuous EEG (CEEG) monitoring is used with increasing frequency to identify electrographic seizures in critically ill children, but studies of current CEEG practice have not been conducted. We aimed to describe the clinical utilization of CEEG in critically ill children at tertiary care hospitals with a particular focus on variables essential for designing feasible prospective multi-center studies evaluating the impact of electrographic seizures on outcome. Methods Eleven North American centers retrospectively enrolled 550 consecutive critically ill children who underwent CEEG. We collected data regarding subject characteristics, CEEG indications, and CEEG findings. Key Findings CEEG indications were encephalopathy with possible seizures in 67% of subjects, event characterization in 38% of subjects, and management of refractory status epilepticus in 11% of subjects. CEEG was initiated outside routine work hours in 47% of subjects. CEEG duration was <12 hours in 16%, 12-24 hours in 34%, and >24 hours in 48%. Substantial variability existed among sites in CEEG indications and neurologic diagnoses, yet within each acute neurologic diagnosis category a similar proportion of subjects at each site had electrographic seizures. Electrographic seizure characteristics including distribution and duration varied across sites and neurologic diagnoses. Significance These data provide a systematic assessment of recent CEEG use in critically ill children and indicate variability in practice. The results suggest that multi-center studies are feasible if CEEG monitoring pathways can be standardized. However, the data also indicate that electrographic seizure variability must be considered when designing studies addressing the impact of electrographic seizures on outcome. PMID:23848569

  5. Developing measurement indices to enhance protection and resilience of critical infrastructure and key resources.

    PubMed

    Fisher, Ronald E; Norman, Michael

    2010-07-01

    The US Department of Homeland Security (DHS) is developing indices to better assist in the risk management of critical infrastructures. The first of these indices is the Protective Measures Index - a quantitative index that measures overall protection across component categories: physical security, security management, security force, information sharing, protective measures and dependencies. The Protective Measures Index, which can also be recalculated as the Vulnerability Index, is a way to compare differing protective measures (eg fence versus security training). The second of these indices is the Resilience Index, which assesses a site's resilience and consists of three primary components: robustness, resourcefulness and recovery. The third index is the Criticality Index, which assesses the importance of a facility. The Criticality Index includes economic, human, governance and mass evacuation impacts. The Protective Measures Index, Resilience Index and Criticality Index are being developed as part of the Enhanced Critical Infrastructure Protection initiative that DHS protective security advisers implement across the nation at critical facilities. This paper describes two core themes: determination of the vulnerability, resilience and criticality of a facility and comparison of the indices at different facilities. PMID:20826384

  6. High critical current density YBa 2Cu 3O 7- δ tapes prepared by the surface-oxidation epitaxy method

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kaname; Kim, SeokBeom; Hirabayashi, Izumi; Watanabe, Tomonori; Uno, Naoki; Ikeda, Masaru

    2000-03-01

    YBa 2Cu 3O 7- δ (YBCO) films with high critical current density ( Jc) were successfully fabricated on nickel tapes buffered with epitaxial NiO. NiO was prepared on the textured nickel tape by the surface-oxidation epitaxy (SOE) method. We have reported so far a critical temperature ( Tc) of 87 K and Jc=4-6×10 4 A/cm 2 (77 K, 0 T) for the YBCO films on NiO/Ni tapes. To enhance the superconducting properties of the YBCO films on the SOE-grown NiO, depositions of thin oxide cap layers such as YSZ, CeO 2, and MgO on NiO were investigated. These oxide cap layers were epitaxially grown on NiO and provided the template for the epitaxial growth of YBCO films. Substantially improved data of Tc=88 K and Jc=3×10 5 A/cm 2 (77 K, 0 T) and 1×10 4 A/cm 2 (77 K, H∥ c, 4 T) were obtained for YBCO film on NiO, by using a MgO cap layer with a thickness of 50 nm. The method described in this paper is a simple way to produce long YBCO tape conductors with high- Jc values.

  7. Critical assessment of enhancement factor measurements in surface-enhanced Raman scattering on different substrates.

    PubMed

    Rodrigues, Daniel C; de Souza, Michele L; Souza, Klester S; dos Santos, Diego P; Andrade, Gustavo F S; Temperini, Marcia L A

    2015-09-01

    The SERS enhancement factor (SERS-EF) is one of the most important parameters that characterizes the ability of a given substrate to enhance the Raman signal for SERS applications. The comparison of SERS intensities and SERS-EF values across different substrates is a common practice to unravel the performance of a given substrate. In this study, it is shown that such a comparison may lack significance if we compare substrates of very distinct nature and optical properties. It is specifically shown that the SERS-EF values for static substrates (e.g. immobilized metallic nanostructures) cannot be compared to those of dynamic ones (e.g. colloidal metal nanoparticle solutions), and that the optical properties for the latter show strong dependence on the metal-molecule interaction dynamics. The most representative experimental results concerning the dynamic substrates have been supported by generalized Mie theory simulations, which are tools used to describe the substrate complexity and the microscopic information not usually taken into account. PMID:25669424

  8. Current developments using emerging transdermal technologies in physical enhancement methods.

    PubMed

    Nanda, A; Nanda, S; Ghilzai, N M Khan

    2006-07-01

    Transdermal drug delivery using patches offers many advantages, but is limited primarily by the stratum corneum barrier. Amongst the various methods to overcome this barrier, physical methods are gaining in popularity and commercial devices development. Macroflux, MTS and Silex are based on microporation, involving use of microneedles that pierce thereby bypassing the stratum corneum. Intraject , Powderject and Helios are based on needleless jet injectors wherein very fine, solid particulate drug, is fired directly into the skin, using high-pressure gas. Med- Tats incorporate use of modified drug-containing tattoos, which bind to the skin, wherein the drug is absorbed. CHADD is based on use of heat, which increases skin - permeation of drugs. High-power, pulsed lasers transmit positive mechanical forces to the skin and create intercellular channels into the skin transiently. Sonophoresis involves use of ultrasound, which transiently disrupts the stratum corneum barrier. This technique offers a non-invasive transdermal extraction of interstitial fluids of sampling body fluids. Modified Liposomes include Ethosomes (containing alcohol) and Transferosomes (containing surfactants), which have enhanced skin permeability. Pulsed magnetic fields may create transient pores in cell membranes, including skin, resulting in increased permeation. Iontophoresis is based on application of electric potential for enhancing the movement of substances to and from the body. Dupel, Ionzyme, Liposite, ETrans, Phoresor and Drionic are based on iontophoresis. GlucoWatch offers non-invasive blood glucose monitoring, based on reverse iontophoresis. This review outlines recent commercial developments in physical transdermal drug delivery technology and the specific devices and applications being targeted by the pharmaceutical industry. PMID:16848725

  9. Orientation-dependent critical currents in Y sub 1 Ba sub 2 Cu sub 3 O sub 7-x epitaxial thin films: Evidence for intrinsic flux pinning

    SciTech Connect

    Christen, D.K.; Klabunde, C.E.; Feenstra, R.; Lowndes, D.H.; Norton, D.P.; Budai, J.D.; Kerchner, H.R.; Thompson, J.R.; Zhu, S. ); Marwick, A.D. )

    1990-01-01

    For YBCO epitaxial thin films the basal plane transport critical current density J{sub c}, flowing perpendicular to an applied magnetic field H, depends sensitively on the orientation of the crystal with respect to H. In particular, J{sub c} is sharply peaked and greatly enhanced when H is precisely parallel to the copper-oxygen planes. Experiments on a series of epitaxial monolithic and superconductor-insulator multilayer thin films provide clear evidence that the enhancement is a bulk, rather than surface or thin sample, phenomenon. Measurements of the orientation dependence are presented and compared with a model of intrinsic flux pinning'' by the layered crystal structure.

  10. Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors

    PubMed Central

    Goodrich, LF; Cheggour, N; Stauffer, TC; Filla, BJ; Lu, XF

    2013-01-01

    We review variable-temperature, transport critical-current (Ic) measurements made on commercial superconductors over a range of critical currents from less than 0.1 A to about 1 kA. We have developed and used a number of systems to make these measurements over the last 15 years. Two exemplary variable-temperature systems with coil sample geometries will be described: a probe that is only variable-temperature and a probe that is variable-temperature and variable-strain. The most significant challenge for these measurements is temperature stability, since large amounts of heat can be generated by the flow of high current through the resistive sample fixture. Therefore, a significant portion of this review is focused on the reduction of temperature errors to less than ±0.05 K in such measurements. A key feature of our system is a pre-regulator that converts a flow of liquid helium to gas and heats the gas to a temperature close to the target sample temperature. The pre-regulator is not in close proximity to the sample and it is controlled independently of the sample temperature. This allows us to independently control the total cooling power, and thereby fine tune the sample cooling power at any sample temperature. The same general temperature-control philosophy is used in all of our variable-temperature systems, but the addition of another variable, such as strain, forces compromises in design and results in some differences in operation and protocol. These aspects are analyzed to assess the extent to which the protocols for our systems might be generalized to other systems at other laboratories. Our approach to variable-temperature measurements is also placed in the general context of measurement-system design, and the perceived advantages and disadvantages of design choices are presented. To verify the accuracy of the variable-temperature measurements, we compared critical-current values obtained on a specimen immersed in liquid helium (“liquid” or Ic liq) at