2,365 results on '"Dou, S."'
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2. Full-wavefield inversion of surface waves for mapping embedded low-velocity zones in permafrost
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Dou, S and Ajo-Franklin, JB
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Geochemistry & Geophysics ,Geophysics - Abstract
Surface waves are advantageous for mapping seismic structures of permafrost, in which irregular velocity gradients are common and thus the effectiveness of refraction methods are limited. Nevertheless, the complex velocity structures that are common in permafrost environments often yield unusual dispersion spectra, in which higher-order and leaky modes are dominant. Such unusual dispersion spectra were prevalent in the multichannel surface-wave data acquired fromour permafrost study site at Barrow, Alaska. Owing to the difficulties in picking and identifying dispersion curves from these dispersion spectra, conventional surface-wave inversion methods become problematic to apply. To overcome these difficulties, we adopted a full-wavefield method to invert for velocitymodels that can best fit the dispersion spectra instead of the dispersion curves. The inferred velocity models were consistent with collocated electric resistivity results and with subsequent confirmation cores, which indicated the reliability of the recovered seismic structures. The results revealed embedded low-velocity zones underlying the ice-rich permafrost at our study site - an unexpected feature considering the low ground temperatures of -10°C to -8°C. The low velocities in these zones (~70%-80% lower than the overlying ice-rich permafrost) were most likely caused by saline pore-waters that prevent the ground from freezing, and the resultant velocity structures are vivid examples of complex subsurface properties in permafrost terrain. We determined that full-wavefield inversion of surface waves, although carrying higher computational costs than conventional methods, can be an effective tool for delineating the seismic structures of permafrost.
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- 2021
3. Prevention of Contact Dermatitis
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Dou, S. H., primary and Maibach, H. I., additional
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- 2022
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4. Investigation of bending behavior for slotted sandwich panels made with ABS and PLA along with aluminum cores
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Dou, S. S., Xia, J. S., Qiu, X. L., and Al-Bahrani, Mohammed
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- 2023
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5. An effective-medium model for P-wave velocities of saturated, unconsolidated saline permafrost
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Dou, S, Nakagawa, S, Dreger, D, and Ajo-Franklin, J
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Geochemistry & Geophysics ,Geophysics - Abstract
To better understand the relationship between P-wave velocities and ice content in saturated, unconsolidated saline permafrost, we constructed an effective-medium model based upon ultrasonic P-wave data that were obtained from earlier laboratory studies. The model uses a two-end-member mixing approach in which an ice-filled, fully frozen end member and a water-filled, fully unfrozen end member are mixed together to form the effective medium of partially frozen sediments. This mixing approach has two key advantages: (1) It does not require parameter tuning of the mixing ratios, and (2) it inherently assumes mixed pore-scale distributions of ice that consist of frame-strengthening (i.e., cementing and/or loadbearing) ice and pore-filling ice. The model-predicted P-wave velocities agree well with our laboratory data, demonstrating the effectiveness of the model for quantitatively inferring ice content from P-wave velocities. The modeling workflow is simple and is largely free of calibration parameters -attributes that ease its application in interpreting field data sets.
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- 2017
6. Relationship Between Proteinase with a Disintegrin and a Metalloproteinase Domain-9 (ADAM9), Inflammation, Airway Remodeling, and Emphysema in COPD Patients
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Cui L, Li H, Xie M, Xu X, Zhang YM, Wang W, Dou S, and Xiao W
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chronic obstructive pulmonary disease ,proteinase with a disintegrin and a metalloproteinase domain-9 ,computed tomography ,emphysema ,airway remodeling ,Diseases of the respiratory system ,RC705-779 - Abstract
Liwei Cui,1 Haijun Li,2 Mengshuang Xie,1 Xia Xu,2 Yingmei Zhang,3 Wei Wang,1 Shuang Dou,1 Wei Xiao1 1Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People’s Republic of China; 2Department of Cadre Health Care, Qilu Hospital, Shandong University, Jinan, People’s Republic of China; 3Department of Pulmonary Medicine, Linyi People’s Hospital, Linyi, People’s Republic of ChinaCorrespondence: Wei XiaoDepartment of Pulmonary Medicine, Qilu Hospital, Shandong University, 107 Wenhuaxi Road, Jinan 250012, People’s Republic of ChinaEmail xiaowei4226@163.comBackground and Objective: The link between ADAM9 and airway remodeling and emphysema severity in COPD patients has not been elucidated. Here, we investigated the relationship between ADAM9 levels in sputum and airway epithelium and the clinical characteristics of COPD patients.Methods: A sputum cohort and a lung tissue cohort were included in the study. Pulmonary function and computed tomography data were analyzed in COPD patients, non-COPD smokers, and non-smokers. Soluble ADAM9 and interleukin 8 (IL-8) levels in sputum supernatants as well as surface ADAM9 expression in airway epithelium were detected. Emphysema scores were calculated by the percentage of low attenuation area (%LAA-950), and airway remodeling was measured via airway thickening and loss of airway counts.Results: Both soluble ADAM9 levels in sputum and relative surface ADAM9 expression in airway epithelium were increased in COPD patients. Sputum ADAM9 levels were negatively correlated with forced expiratory volume in 1 s of predicted (FEV1% of predicted) and positively correlated with sputum IL-8 levels, but not with CT measured emphysema nor airway remodeling. The ADAM9 expression in airway epithelia was positively correlated with %LAA-950 and airway wall thickening parameters (wall area percentage, WA%; the square root of the wall area in a standard airway with a 10 mm internal perimeter, Pi-10), while negatively correlated with airway counts derived from the 4th to 9th bronchial generations.Conclusion: Airway ADAM9 levels in sputum and airway epithelium were both elevated in COPD patients compared to non-COPD controls. Sputum ADAM9 seemed to be associated with inflammatory responses in COPD, while epithelial ADAM9 was more correlated with emphysema and airway remodeling.Keywords: chronic obstructive pulmonary disease, proteinase with a disintegrin and a metalloproteinase domain-9, computed tomography, emphysema, airway remodeling
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- 2020
7. Analysis of laboratory data on ultrasonic monitoring of permeability reduction due to biopolymer formation in unconsolidated granular media
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Berryman, JG, Kwon, T‐H, Dou, S, Ajo‐Franklin, JB, and Hubbard, SS
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Permeability reduction ,Geophysics ,Computation Theory and Mathematics ,Geochemistry & Geophysics - Abstract
We show how to estimate the fluid permeability changes due to accumulated biopolymer within the pore space of a granular material using laboratory measurements of overall permeability, together with various well-known quantitative measures (e.g., porosity, specific surface area, and formation factor) of the granular medium microstructure. The main focus of the paper is on mutual validation of existing theory and a synthesis of new experimental results. We find that the theory and data are in good agreement within normal experimental uncertainties. We also establish quantitative empirical relationships between seismic and/or acoustic attenuation and overall permeability for these same systems.
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- 2016
8. P1.27-05 Two- and Three-dimensional Radiomic Measurements for Clinical Stage IA Lung Adenocarcinoma: Less is More
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Wang, M.-M., primary, Dou, S.-H., additional, Li, H.-J., additional, Wu, Y.-L., additional, Yang, L., additional, and Zhong, W.-Z., additional
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- 2023
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9. Enhancement of Transition Temperature in FexSe0.5Te0.5 Film via Iron Vacancies
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Zhuang, J. C., Yeoh, W. K., Cui, X. Y., Kim, J. H., Shi, D. Q., Shi, Z. X., Ringer, S. P., Wang, X. L., and Dou, S. X.
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Condensed Matter - Superconductivity - Abstract
The effects of iron deficiency in FexSe0.5Te0.5 thin films (0.8
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- 2014
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10. On the roles of graphene oxide doping for enhanced supercurrent in MgB2 based superconductors
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Yeoh, W. K., Cui, X. Y., Gault, B., De Silva, K. S. B., Xu, X., Liu, H. W., Yen, H. W., Wong, D., Bao, P., Larson, D. J., Martin, I., Li, W. X., Zheng, R. K., Wang, X. L., Dou, S. X., and Ringer, S. P.
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Condensed Matter - Superconductivity ,Condensed Matter - Materials Science - Abstract
Due to their graphene-like properties after oxygen reduction, incorporation of graphene oxide (GO) sheets into correlated-electron materials offers a new pathway for tailoring their properties. Fabricating GO nanocomposites with polycrystalline MgB2 superconductors leads to an order of magnitude enhancement of the supercurrent at 5 K/8 T and 20 K/4 T. Herein, we introduce a novel experimental approach to overcome the formidable challenge of performing quantitative microscopy and microanalysis of such composites, so as to unveil how GO doping influences the structure and hence the material properties. Atom probe microscopy and electron microscopy were used to directly image the GO within the MgB2, and we combined these data with computational simulations to derive the property-enhancing mechanisms. Our results reveal synergetic effects of GO, namely, via localized atomic (carbon and oxygen) doping as well as texturing of the crystals, which provide both inter and intra granular flux pinning. This study opens up new insights into how low-dimensional nanostructures can be integrated into composites to modify the overall properties, using a methodology amenable to a wide range of applications.
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- 2014
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11. Transport evidence of robust topological surface state in BiTeCl single crystals, the first strong inversion asymmetric topological insulator
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Xiang, F. X., Wang, X. L., and Dou, S. X.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science ,Condensed Matter - Other Condensed Matter - Abstract
Three-dimensional (3D) topological insulators (TIs) are new forms of quantum matter that are characterized by their insulating bulk state and exotic metallic surface state, which hosts helical Dirac fermions1-2. Very recently, BiTeCl, one of the polar semiconductors, has been discovered by angle-resolved photoemission spectroscopy to be the first strong inversion asymmetric topological insulator (SIATI). In contrast to the previously discovered 3D TIs with inversion symmetry, the SIATI are expected to exhibit novel topological phenomena, including crystalline-surface-dependent topological surface states, intrinsic topological p-n junctions, and pyroelectric and topological magneto-electric effects3. Here, we report the first transport evidence for the robust topological surface state in the SIATI BiTeCl via observation of Shubnikov-de Haas (SdH) oscillations, which exhibit the 2D nature of the Fermi surface and pi Berry phase. The n = 1 Landau quantization of the topological surface state is observed at B . 12 T without gating, and the Fermi level is only 58.8 meV above the Dirac point, which gives rise to small effective mass, 0.055me, and quite large mobility, 4490 cm2s-1. Our findings will pave the way for future transport exploration of other new topological phenomena and potential applications for strong inversion asymmetric topological insulators., Comment: 10 pages, 3 figures, 1 table, references updated
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- 2014
12. Reaction method control of impurity scattering in C-doped MgB2, proving the role of defects besides C substitution level
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Chen, S K, Tan, K Y, Halim, A S, Xu, X, De Silva, K S B, Yeoh, W K, Dou, S X, Kursumovic, A, and MacManus-Driscoll, J L
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Condensed Matter - Superconductivity - Abstract
In this study, Si and C were incorporated into polycrystalline MgB2 via in situ reaction of Mg and B with either SiC or with separate Si and C (Si+C). The electrical transport and magnetic properties of the two series of samples were compared. The corrected resistivity at 40K, Rho A(40K), is higher for the SiC reacted samples regardless of carbon (C) substitution level, indicating larger intragrain scattering because of the simultaneous reaction between Mg and SiC and carbon substitution during the formation of MgB2. In addition, because of the cleaner reaction route for the SiC reacted samples, the calculated active area that carries current, AF, is twice that of the (Si+C) samples. On the other hand, the upper critical field, Hc2, was similar for both sets of samples despite their different C substitution levels which proves the importance of defect scattering in addition to C substitution level. Hence, the form of the precursor reactants is critical for tuning the form of Hc2(T)., Comment: accepted for publication
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- 2013
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13. Abnormal Magnetic Behaviors in Unique Square alpha-MnO2 Nanotubes
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Zeng, R., Wang, J. Q., Li, W. X., Du, G. D., Chen, Z. X., Li, S., and Dou, S. X.
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Condensed Matter - Materials Science - Abstract
Systematic magnetic measurements have been performed in unique$\alpha - MnO_2$ square nanotubes synthesized by a facile hydrothermal method with microwave-assisted procedures. Unusual magnetic phenomena (abnormal magnetization verse temperature (M - T) behaviour, large and abnormal magnetization hysteresis loop horizontal shift (HHS) verse cooling field (HFC) behaviours (HHS - HFC) has been observed in these square nanotubes. These suggest the observation of large unfrozen orbital moment which also is the micro -original of observed large and abnormal horizontal shift (HHS). The findings demonstrated that engineering layered structures in nanoscale would create many unique nanostructures and unusual physicochemical behaviours., Comment: 23 Pgs, 10 Figs
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- 2012
14. Architected Various MnO6 Octahedral Layers MnO2 Nanostructures
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Zeng, R., Wang, J. Q., Du, G. D., Li, W. X., Chen, Z. X., Li, S., and Dou, S. X.
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
A series of MnO2 unique nanostructures were synthesized by a facile hydrothermal method with microwave-assisted procedures. A novel nanostructure formation mechanism has been proposed, that MnO6 octahedral nuclei and molecular layers can be rearranged into different nanostructured morphologies by restacking and splitting, and then clasping, which is associated with tunnel structure phase transformation. Systematic macrostructure observations and magnetic property measurements have been conducted on these nanostructures, which demonstrate that engineering layered structures has the potential to create many unique nanostructures and unusual physicochemical behaviours., Comment: 15 Pgs, 7 Figs
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- 2012
15. Extremely Large Magnetic Entropy Changes, Quantum Phases, Transitions and Diagram in Gd(OH)3 Single Crystal Nanowires - Quasi-1D Large Spin (S = -7/2) Chain Antiferromagnet
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Zeng, R., Zhang, C. F., Debnath, J. C., Shamba, P., Wang, J. L., Chen, Z. X., Guo, Z. P., and Dou, S. X.
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Condensed Matter - Materials Science - Abstract
Systematically magnetic and magnetothermal measurements at temperatures down to 2 K and magnetic fields up to 13.5 Tesla for Gd(OH)3 Single Crystal Nanowires - Quasi-1D Large Spin (S = -7/2) Chain Antiferromagnet have been conducted. We find that, (1) magnetic field enhances the thermal and local spin fluctuations which suppress long-range spin ordering (LRO) within the measured temperature range, and close to 0 K at the quantum critical point (QCP); (2) possible field-induced exotic local spin-liquid-like, aligned-spin, and spin-flip exotic paramagnetic phases, and transitions in the low temperature and high field range have been observed, allowing us to identify a possible quantum critical point; (3) there is extremely large, fully reversible MCE (magnetic entropy change (-{\Delta}SM) = 27.8, 66, and 88 J / kg K, adiabatic temperature change ({\Delta}Tad) = 6.7, 17.6, and 36.4 K at 2.55 K for field changes of 2, 5, and 11 T, respectively in the continuum of quantum phase transitions in this system; (4) moreover, careful experiments and analysis may allow experimental determination and set up a quantum phase diagram of this system. The magnetic-entropy change monotonically increases with decreasing temperature, and it exceeds the magnetocaloric effect (MCE) in any other known low temperature reversible MCE material by at least a factor of 3. The extremely large magnetic entropy change may be attributed to the large amount of weakly interacting spins that can be easily aligned at low-lying energy in the quantum critical regime of our nanosized materials, since there is large MCE in the local spin-liquid-like (low energy excitation and even gapless state) range. These indicate that the material is a promising MCE candidate for low temperature application, and possibly could make ultra-low temperatures easily achievable for most laboratories and for space application as well., Comment: 32 pages, 13 figures
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- 2012
16. {110} Plane Orientation Driven Superior Li-ion Battery Performance and Room Temperature Ferromagnetism in Co3O4 Nanostructures
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Zeng, R., Wang, J. Q., Du, G. D., Li, W. X., Chen, Z. X., Li, S., Guo, Z. P., and Dou, S. X.
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Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
This paper presents synthesis methods and multifunctional properties of porous Co3O4 nanoplatelets and nanowires. Surprisingly, significantly superior Li-ion battery performance compared to other cathode materials is exhibited in the same samples as room temperature ferromagnetism (RTFM). Microstructure observations, and properties measurements and analysis indicate that the as-prepared Co3O4 nanostructures exhibit a spontaneous transformation of their morphology, showing a predominantly {110} plane orientation and preferentially presenting the Co3+ species at the surface at appreciate preparation condition. More Co3+ in an octahedral (O) position exposed on the surface is associated with more Co3+ being Co3+|\cdot (Co3+ with trapped charge carriers) or reduced to Co2+ in the O position due to surface defects or oxygen vacancies, which is possibly the mechanism of excellent electric transport properties then high Li-battery performance; at the same time, reduced to Co2+ or free charge carriers trapped by Co3+|\cdot in the O position are the role of charge carries- mediate ferromagnetism, may be the origin of RTFM as well. These results further show the importance of modifying the nanostructure of surfaces in the preparation of transition metal oxides as multidisciplinary functional materials., Comment: 34 pages, 25 figures. arXiv admin note: text overlap with arXiv:0903.5214 by other authors
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- 2012
17. Domain Wall Conductivity in Oxygen Deficient Multiferroic YMnO3 Single Crystals
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Du, Y., Wang, X. L., Chen, D. P., Dou, S. X., Cheng, Z. X., Higgins, M., Wallace, G., and Wang, J. Y.
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Condensed Matter - Materials Science - Abstract
The transport properties of domain walls in oxygen deficient multiferroic YMnO3 single crystals have been probed using conductive atomic force microscopy and piezoresponse force microscopy. Domain walls exhibit significantly enhanced conductance after being poled in electric fields, possibly induced by oxygen vacancy ordering at domain walls. The electronic conduction can be understood by the Schottky emission and Fowler-Nordheim tunnelling mechanisms. Our results show that the domain wall conductance can be modulated through band structure engineering by manipulating ordered oxygen vacancies in the poling fields., Comment: 4 pages, 4 figures; Applied Physics Letters (2011)
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- 2012
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18. Simulation of light C4+ ion irradiation and its significant enhancement to the critical current density in BaFe1.9Ni0.1As2 single crystals
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Shahbazi, M., Wang, X. L., Ionescu, M., Ghorbani, S. R., Dou, S. X., Choi, K. Y., and Chung, K. K.
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Condensed Matter - Superconductivity - Abstract
In this work, we report the simulation of C4+ irradiation and its significant effects towards the enhancement of the critical current density in BaFe1.9Ni0.1As2 single crystals. BaFe1.9Ni0.1As2 single crystals with and without the C-implantation were characterized by magneto-transport and magnetic measurements up to 13 T over a wide range of temperatures below and above the superconducting critical temperature, Tc. It is found that the C-implantation causes little change in Tc, but it can greatly enhance the in-field critical current density by a factor of up to 1.5 with enhanced flux jumping at 2 K. Our Monte Carlo simulation results show that all the C ions end up in a well defined layer, causing extended defects and vacancies at the layer, but few defects elsewhere on the implantation paths. This type of defect distribution is distinct from the columnar defects produced by heavy ion implantation. Furthermore, the normal state resistivity is enhanced by the light C4+ irradiation, while the upper critical field, Hc2, the irreversibility field, Hirr, and Tc were affected very little., Comment: 14 [pages, 7 figures
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- 2011
19. Vortex glass line and vortex liquid resistivity in doped BaFe2As2 single crystals
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Ghorbani, S. R., Wang, X. L., Shabazi, M., Dou, S. X., Choi, K. Y., and Lin, C. T.
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Condensed Matter - Superconductivity - Abstract
The vortex liquid-to-glass transition has been studied in Ba0.72K0.28Fe2As2, Ba0.9Co0.1Fe2As2, and Ba(Fe0.45Ni0.05)2As2 single crystal with superconducting transition temperature, Tc = 31.7, 17.3, and 18 K, respectively, by magnetoresistance measurements. For temperatures below Tc, the resistivity curves were measured in magnetic fields within the range of 0 \leq B \leq 13 T, and the pinning potential was scaled according to a modified model for vortex liquid resistivity. Good scaling of the resistivity {\rho}(B, T) and the effective pinning energy U0(B,T) was obtained with the critical exponents s and B0. The vortex state is three-dimensional at temperatures lower than a characteristic temperature T*. The vortex phase diagram was determined based on the evolution of the vortex-glass transition temperature Tg with magnetic field and the upper critical field, Hc2. We found that non-magnetic K doping results in a high glass line close to the Hc2, while magnetic Ni and Co doping cause a low glass line which is far away from the Hc2. Our results suggest that non-magnetic induced disorder is more favourable for enhancement of pinning strength compared to magnetic induced disorder. Our results show that the pinning potential is responsible for the difference in the glass states., Comment: 4 pages, 6 figures, submitted
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- 2011
20. Direct observation of local K variation and its correlation to electronic inhomogeneity in (Ba1-xKx)Fe2As2 Pnictide
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Yeoh, W. K., Gault, B., Cui, X. Y., Zhu, C., Moody, M. P., Li, L., Zheng, R. K., Li, W. X, Wang, X. L., Dou, S. X., Lin, C. T., and Ringer, S. P.
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Condensed Matter - Superconductivity - Abstract
Local fluctuations in the distribution of dopant atoms are a suspected cause of nanoscale electronic disorder or phase separation observed within the pnictide superconductors. Atom probe tomography results present the first direct observations of dopant nano-clustering in a K-doped 122-phase pnictides. First-principles calculations suggest the coexistence of static magnetism and superconductivity on a lattice parameter length scale over a large range of doping concentrations. Collectively, our results provide evidence for a mixed scenario of phase coexistence and phase separation originating from variation of dopant atom experiments distroibutions., Comment: 4 pages, 4 figures and 1 table, accepted by Physical Review Letter 2011
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- 2011
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21. Very strong intrinsic supercurrent carrying ability and vortex avalanches in (Ba,K)Fe2As2 superconducting single crystals
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Wang, Xiao-Lin, Ghorbani, S. R., Lee, Sung-Ik, Dou, S. X., Lin, C. T., Johansen, T. H., Cheng, Z. X., Peleckis, G., Muller, K., Shabazi, M., Sun, G. L., and Sun, D. L.
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Condensed Matter - Superconductivity ,Condensed Matter - Strongly Correlated Electrons - Abstract
We report that single crystals of (Ba,K)Fe2As2 with Tc = 32 K have a pinning potential, U0, as high as 10^4 K, with U0 showing very little field depend-ence. In addition, the (Ba,K)Fe2As2 single crystals become isotropic at low temperatures and high magnetic fields, resulting in a very rigid vortex lattice, even in fields very close to Hc2. The rigid vortices in the two dimensional (Ba,K)Fe2As2 distinguish this compound from 2D high Tc cuprate superconductors with 2D vortices, and make it being capable of cearrying very high critical current.Flux jumping due to high Jc was also observed in large samples at low temperatures., Comment: 4 pages, 7 figures. submitted
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- 2010
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22. Graphene doping to enhance flux pinning and supercurrent carrying ability in magnesium diboride superconductor
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Xu, X., Dou, S. X., Wang, X. L., Kim, J. H., Stride, J. A., Choucair, M., Yeoh, W. K., Zheng, R. K., and Ringer, S. P.
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Condensed Matter - Superconductivity - Abstract
It has been shown that graphene doping is sufficient to lead to an improvement in the critical current density - field performance (Jc(B)), with little change in the transition temperature in MgB2. At 3.7 at% graphene doping of MgB2 an optimal enhancement in Jc(B) was reached by a factor of 30 at 5 K and 10 T, compared to the un-doped sample. The results suggested that effective carbon substitutions by grapheme, 2D nature of grapheme and the strain effect induced by difference thermal coefficient between single grapheme sheet and MgB2 superconductor may play an important role in flux pinning enhancement.
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- 2010
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23. Lattice paramenter, lattice disorder and resistivity of carbohydrate doepd MgB2 and their correlation with the transition temperature
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Kim, J. H., Oh, Sangjun, Xu, X., Joo, Jinho, Rindflesich, M., Tomsic, M., and Dou, S. X.
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Condensed Matter - Superconductivity - Abstract
The change in the lattice parameters or the lattice disorder is claimed as a cause of the slight reduction in the transition temperature by carbon doping in MgB2. In this work, an extensive investigation on the effects of carbohydrate doping has been carried out. It is found that not only the a-axis but also the c-axis lattice parameter increases with the sintering temperature. A linear relation between the unit cell volume and the critical temperature is observed. Compared with the well known correlation between the lattice strain and the critical temperature, the X-ray peak broadening itself shows a closer correlation with the transition temperature. The residual resistivity and the critical temperature are linearly correlated with each other as well and its implication is further discussed., Comment: 3 pages. Accepted by Jouranl of nanoscience and Nanotechnology (JNN)
- Published
- 2009
24. Enhancement of the in-field Jc of MgB2 via SiCl4 doping
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Wang, Xiao-Lin, Dou, S. X., Hossain, M. S. A., Cheng, Z. X., Liao, X. Z., Ghorbani, S. R., Yao, Q. W., Kim, J. H., and Silver, T.
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Condensed Matter - Superconductivity ,Condensed Matter - Materials Science - Abstract
In this work, we present the following important results: 1) We introduce a new Si source, liquid SiCl4, which is free of C, to significantly enhance the irreversibility field (Hirr), the upper critical field (Hc2), and the critical current density (Jc), with little reduction in the critical temperature (Tc). 2) Although Si can not incorporate into the crystal lattice, we found a reduction in the a-axis lattice parameter, to the same extent as for carbon doping. 3) The SiCl4 treated MgB2 shows much higher Jc with superior field dependence above 20 K than undoepd MgB2 and MgB2 doped with various carbon sources. 3) We provide an alternative interpretation for the reduction of the a lattice parameter in C- and non-C doped MgB2. 4). We introduce a new parameter, RHH (Hc2/Hirr), which can clearly reflect the degree of flux pinning enhancement, providing us with guidance for further enhancing Jc. 5) We have found that spatial variation in the charge carrier mean free path is responsible for the flux pinning mechanism in the SiCl4 treated MgB2 with large in-field Jc., Comment: 18 pages, 9 figures
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- 2009
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25. Correlation between doping induced disorder and superconducting properties in carbohydrate doped MgB2
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Kim, J. H., Dou, S. X., Oh, Sangjun, Jercinovic, M., Babic, E., Nakane, T., and Kumakura, H.
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Condensed Matter - Superconductivity - Abstract
A comprehensive study of the effects of carbohydrate doping on the superconductivity of MgB2 has been conducted. In accordance with the dual reaction model, more carbon substitution is achieved at lower sintering temperature. As the sintering temperature is lowered, lattice disorder is increased. Disorder is an important factor determining the transition temperature for the samples studied in this work, as evidenced from the correlations among the lattice strain, the resistivity and the transition temperature. It is further shown that the increased critical current density in the high field region can be understood by a recently-proposed percolation model [Phys. Rev. Lett. 90 (2003) 247002]. For the critical current density analysis, the upper critical field is estimated from a correlation that has been reported in a recent review article [Supercond. Sci. Technol. 20 (2007) R47], where a sharp increase in the upper critical field by doping is mainly due to an increase in lattice disorder or impurity scattering. On the other hand, it is shown that the observed reduction in self-field critical current density is related to the reduction in the pinning force density by carbohydrate doping., Comment: 5 pages, 3 figures
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- 2008
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26. Unconventional superconductivity of NdFeAsO0.82F0.18 indicated by the low temperature dependence of the lower critical field Hc1
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Wang, X. L., Dou, S. X., Ren, Zhi-An, Yi, Wei, Li, Zheng-Cai, Zhao, Zhong-Xian, and Lee, Sung-IK
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Condensed Matter - Superconductivity ,Condensed Matter - Materials Science - Abstract
We measured the initial M-H curves for a sample of the newly discovered superconductor NdFeAsO0.82Fe0.18, which had a critical temperature, Tc, of 51 K, and was fabricated at the high pressure of 6 GPa. The lower critical field, Hc1, was extracted from the deviation point of the Meissner linearity in the M-H curves, which show linear temperature dependence in the low temperature region down to 5 K. The Hc1(T) indicates no s-wave superconductivity, but rather an unconventional superconductivity with a nodal gap structure. Furthermore, the linearity of Hc1 at low temperature does not hold at high temperature, but shows other characteristics, indicating that this superconductor might have multi-gap features. Based on the low temperature nodal gap structure, we estimate that the maximum gap magnitude delta 0 = (1.6+- 0.2) kBTc., Comment: 8 pages, 3 figures
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- 2008
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27. Giant Magnetocaloric Effect in Re-entrant Ferromagnet PrMn1.4Fe0.6Ge2
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Zeng, R., Wang, J. L, Lu, L., Li, W. X., Campbell, S. J., and Dou, S. X.
- Subjects
Condensed Matter - Materials Science - Abstract
Three first order magnetic phase transitions (FOMT) have been detected at TCPr, TNinter and TCinter over the temperature range from 5 K to 340 K at fields up to 9 T in PrMn1.4Fe0.6Ge2, and the magnetocaloric effect (MCE) around these transitions evaluated. The MCE of two FOMT from planar antiferromagnetism (AFl) to c-axis ferromagnetism (Fmc) around 168 K, and from the Fmc state to the c-axis AFmc state around 157 K have acceptable values compared with those of existing MCE systems. A giant magnetocaloric effect (GMCE) has been observed around 25.5 K associated with the field-induced FOMT from the AFmc to the Fmc+F(Pr) state with an additional Pr magnetic contribution. The MCE value 29.1 J/kg K with field change 7 T is comparable to and even larger than reported values for the best-performed MCE materials. In particular, the giant MCE value of 12.3 J/kg K obtained for the relatively small field change from 0 to 1 T is very beneficial for applications, and this, together with the small magnetic and thermal hysteresis, suggests that PrMn1.4Fe0.6Ge2 may be a promising candidate for magnetic refrigeration applications in the hydrogen liquefication temperature range.
- Published
- 2008
28. Flux pinning mechanism in NdFeAsO0.82F0.18 superconductor: Thermally activated flux flow and charge carrier mean free path fluctuation pinning
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Wang, X. L., Ghorbani, S. R., Dou, S. X., Shen, Xiao-Li, Yi, Wei, Li, Zheng-Cai, and Ren, Zhi-An
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Condensed Matter - Superconductivity - Abstract
The flux pinning mechanism of NdO0.82F0.18FeAs superconductor made under high pressure, with a critical temperature, Tc, of 51 K, has been investigated in detail in this work. The field dependence of the magnetization and the temperature dependence of the magnetoresistivity were measured in fields up to 13 T. The field dependence of the critical current density, Jc(B), was analyzed within the collective pinning model. A crossover field, Bsb, from the single vortex to the small vortex bundle pinning regime was observed. The temperature dependence of Bsb(T) is in good agreement with the delta-l pinning mechanism, i.e., pinning associated with fluctuations in the charge-carrier mean free path, l. Analysis of resistive transition broadening revealed that thermally activated flux flow is found to be responsible for the resistivity contribution in the vicinity of Tc. The activation energy U0/kB is 2000 K in low fields and scales as B (-1/3) over a wide field range. Our results indicate that the NdO0.82F0.18FeAs has stronger intrinsic pinning than Bi-2212 and also stronger than MgB2 for H > 8 T., Comment: 4 pages, 6 figures. submitted on 8 June 2008
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- 2008
29. Very high critical field and superior Jc-field performance in NdO0.82F0.18FeAs with Tc of 51 K
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Wang, X. L., Ghorbani, R., Peleckis, G., and Dou, S. X.
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Condensed Matter - Superconductivity - Abstract
The discovery of the new family of oxypnictide superconductors, such as LaFeAsO0.89F0.1, with critical temperature, Tc, over 26 K, has brought new impetus to the fields of high temperature superconductivity and strongly correlated electron systems. These materials showed high upper critical fields, Hc2, which have been estimated to be higher than 55 or 63-65 T in LaO0.9F0.1FeAs with Tc of 26 K, 70 T in PrFeAsO0.85F0.15, and over 100 T in SmO0.85F0.15FeAs with Tc of 46 K. The two gap superconductivity proposed for LaO0.9F0.1FeAs suggests that the Hc2 could be further increased to a significant extent. This is one of the unique features of the FeAs based new superconductors. In this work, we show that the Bc2(48 K) = 13 T and the Bc2(0) value can exceed 230 T in a high pressure fabricated NdO0.82F0.18FeAs bulk sample with Tc of 51 K. We also demonstrate that the supercurrent density from 1 up to 9 T only drops by a factor of 2-6 for T < 30 K, much weaker than MgB2 and high Tc cuprate superconductors. The very high Bc2 already far surpasses those of high Tc cuprates, MgB2, and classical low temperature superconductors, paving the way to use the new NdO0.82F0.18FeAs superconductors for high-field applications., Comment: 11 pages, 7 figures
- Published
- 2008
30. Impact of COPD on prognosis of lung cancer: from a perspective on disease heterogeneity
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Wang W, Dou S, Dong W, Xie M, Cui L, Zheng C, and Xiao W
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lung cancer ,COPD ,prognosis ,histology ,disease heterogeneity ,Diseases of the respiratory system ,RC705-779 - Abstract
Wei Wang,1,* Shuang Dou,1,* Wenyan Dong,2 Mengshuang Xie,1 Liwei Cui,1 Chunyan Zheng,1 Wei Xiao1 1Department of Pulmonary Medicine, Qilu Hospital, Shandong University, Jinan, People’s Republic of China; 2Department of Geriatric Medicine, The Second Hospital of Shandong University, Jinan, People’s Republic of China *These authors contributed equally to this work Background: COPD is an important comorbidity of lung cancer, but the impact of COPD on the outcomes of lung cancer remains uncertain. Because both COPD and lung cancer are heterogeneous diseases, we evaluated the link between COPD phenotypes and the prognosis of different histological subtypes of lung cancer.Methods: In this retrospective study, subjects with a newly and pathologically confirmed diagnosis of lung cancer were enrolled from patients preparing for lung cancer surgery. All participants underwent pulmonary function test (PFT). The diagnosis of COPD was based on GOLD criteria. Lung cancer subtypes and COPD phenotypes were categorized by WHO classification of lung tumors and computer quantitative analysis of PFT. The HRs were estimated by Cox regression analysis.Results: Among 2,222 lung cancer patients, 32.6% coexisted with COPD. After adjustment for age, sex, body mass index (BMI), smoking status, and therapy method, COPD was significantly associated with the decreased overall survival (OS) of lung cancer (HR 1.28, 95% CI 1.05–1.57). With the increased severity of COPD, the OS of lung cancer was gradually worsened (HR 1.23, 95% CI 1.08–1.39). But surgical treatment and high BMI were independent prognostic protective factors (HR 0.46, 95% CI 0.37–0.56; HR 0.96, 95% CI 0.94–0.99). Moreover, in terms of disease heterogeneity, emphysema-predominant phenotype of COPD was an independent prognostic risk factor for squamous carcinoma (HR 2.53, 95% CI 1.49–4.30). No significant relationship between COPD phenotype and lung cancer prognosis was observed among adenocarcinoma, small cell lung cancer, large cell lung cancer, and other subtype patients.Conclusion: These findings suggest that COPD, especially emphysema-predominant phenotype, is an independent prognostic risk factor for squamous carcinoma only. Keywords: lung cancer, COPD, prognosis, histology, disease heterogeneity
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- 2018
31. Mechanism of enhancement of electromagnetic properties of MgB2 by nano-SiC doping
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Dou, S. X., Shcherbakova, O., Yeoh, W. K., Kim, J. H., Soltanian, S., Wang, X. L., Senatore, C., Flukiger, R., Dhalle, M., Husnjak, O., and Babic, E.
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Condensed Matter - Superconductivity - Abstract
A comparative study of pure, SiC, and C doped MgB2 wires has revealed that the SiC doping allowed C substitution and MgB2 formation to take place simultaneously at low temperatures. C substitution enhances Hc2, while the defects, small grain size and nanoinclusions induced by C incorporation and low temperature processing are responsible for the improvement in Jc. The irreversibility field (Hirr) for the SiC doped sample reached the benchmarking value of 10 T at 20 K, exceeding that of NbTi at 4.2 K. This dual reaction model also enables us to predict desirable dopants for enhancing the performance properties of MgB2., Comment: 15 pages, 4 figures, 1 table. accepted for publication in Physical Review Letter
- Published
- 2007
32. Improvement of Critical Current Density and Upper Critical Field in MgB2 using Carbohydrate
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Kim, J. H., Hossain, M. S. A., Xu, X., Yeoh, W. K., Shi, D. Q., Dou, S. X., Ryu, S., Rindfleisch, M., and Tomsic, M.
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Condensed Matter - Superconductivity - Abstract
We evaluated the doping effects of carbohydrate (malic acid, C4H6O5), from 0wt% to 30wt% of total MgB2, on the phase, lattice parameters, critical temperature, resistivity, and upper critical field of MgB2 superconductor. The lattice parameters calculated show a large decrease in the a-axis for MgB2 + C4H6O5 samples, but no change in the c-axis. This is an indication of the carbon substitution into boron coming from C4H6O5, resulting in enhancement of resistivity, critical current density, and upper critical field. Specifically, the critical current density value of 25000 Acm2 at 5 K and 8 T for the MgB2 + 30wt% C4H6O5 sample is higher than that of the un-doped MgB2 by a factor of 21. In addition, resistivity value for all the MgB2 + C4H6O5 samples ranged from 80 to 90 microohm centimeter at 40 K, which is higher than for un-doped MgB2. The increased resistivity indicates increased impurity scattering due to carbon, resulting in enhanced upper critical field., Comment: 4 page, 5 figures, ASC2006 conference
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- 2006
33. Enhancement of in-field Jc in MgB2/Fe wire using single and multi-walled nanotubes
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Kim, J. H., Yeoh, W. K., Qin, M. J., Xu, X., Dou, S. X., Munroe, P., Kumakura, H., Nakane, T., and Jiang, C. H.
- Subjects
Condensed Matter - Superconductivity - Abstract
We investigated the doping effects of SWCNTs and MWCNTs on the Tc, lattice parameters, Jc(B), microstructure, and Hc2 of MgB2/Fe wire. These effects systematically showed the following sequence for Tc and the a-axis: the SWCNT doped wire < the MWshortCNT doped wire < the MWlongCNT doped wire < un-doped wire, while Jc(B) followed the sequence of the SWCNT doped wire > the MWshortCNT doped wire > the MWlongCNT doped wire > un-doped wire. A dominating mechanism behind all these findings is the level of C substitution for B in the lattice. The best Jc(B) and Hc2 were obtained on SWCNT doped wire because the level of C substitution for B in this wire is higher than all others., Comment: 18 pages, 4 figures, 2 tables. accepted by applied physics letters
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- 2006
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34. Strong enhancement of critical current density in MgB2 superconductor using carbohydrate doping
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Kim, J. H., Zhou, S., Hossain, M. S. A., Pan, A. V., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity - Abstract
With the relatively high critical temperature (Tc) of 39 K1 and the high critical current density (Jc) of > 100000 A/cm2 in moderate fields, magnesium diboride (MgB2) superconductors could offer the promise of important large-scale and electronic device applications to be operated at 20 K. A significant enhancement in the electromagnetic properties of MgB2 has been achieved through doping with various form of carbon (C). However, doping effect has been limited by the agglomeration of nano-sized dopants and the poor reactivity of C containing dopants with MgB2. Un-reacted dopants result in a reduction of superconductor volume. In this work, we demonstrate the advantages of carbohydrate doping over other dopants, resulting in an increase of in-field Jc by more than one order of magnitude without any degradation of self-field Jc. As there are numerous carbohydrates readily available this finding has significant ramifications not only for the fabrication of MgB2 but also for many C based compounds and composites., Comment: 12 pages, 1 table, 4 figures
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- 2006
35. The doping effect of multiwall carbon nanotube on MgB2/Fe superconductor wire
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Kim, J. H., Yeoh, W. K., Qin, M. J., Xu, X., and Dou, S. X.
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Condensed Matter - Superconductivity - Abstract
We evaluated the doping effect of two types of multiwall carbon nanotube (CNT) with different aspect ratios on MgB2/Fe monofilament wires. Relationships between microstructure, magnetic critical current density (Jc), critical temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) for pure and CNT doped wires were systematically studied for sintering temperature from 650oC to 1000oC. As the sintering temperature increased, Tc for short CNT doped sample slightly decreased, while Tc for long CNT doped sample increased. This indicates better reactivity between MgB2 and short CNT due to its small aspect ratio and substitution of carbon (C) from short CNT for boron (B) occurs. In addition, short CNT doped samples sintered at the high temperatures of 900oC and 1000oC exhibited excellent Jc, and that value was approximately 104 A/cm2 in fields up to 8 T at 5 K. This suggests that short CNT is a promising carbon source for MgB2 superconductor with excellent Jc. In particular, inclusion of nanosized MgO particles and substitution of C into the MgB2 lattice could result in strong flux pinning centers., Comment: 18 pages, 7 figures
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- 2006
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36. Magnetic field processing to enhance critical current densities of MgB2 superconductors
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Dou, S. X., Yeoh, W. K., Shcherbakova, O., Horvat, J., Qin, M. J., Li, Y., Ren, Z. M., and Munroe, P.
- Subjects
Condensed Matter - Superconductivity - Abstract
Magnetic field of up to 12 T was applied during the sintering process of pure MgB2 and carbon nanotube (CNT) doped MgB2 wires. We have demonstrated that magnetic field processing results in grain refinement, homogeneity and significant enhancement in Jc(H) and Hirr. The Jc of pure MgB2 wire increased by up to a factor of 3 to 4 and CNT doped MgB2 by up to an order of magnitude in high field region respectively, compared to that of the non-field processed samples. Hirr for CNT doped sample reached 7.7 T at 20 K. Magnetic field processing reduces the resistivity in CNT doped MgB2, straightens the entangled CNT and improves the adherence between CNTs and MgB2 matrix. No crystalline alignment of MgB2 was observed. This method can be easily scalable for a continuous production and represents a new milestone in the development of MgB2 superconductors and related systems.
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- 2006
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37. Large Upper Critical Field and Irreversibility Field in MgB2 wires with SiC additions
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Sumption, M. D., Bhatia, M., Collings, E. W., Rindfleisch, M., Tomsic, M., Soltanian, S., and Dou, S. X.
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Condensed Matter - Superconductivity - Abstract
Resistive transition measurements are reported for Magnesium diboride strands with SiC dopants. The SiC was added as 10 mol of SiC to 90 mol of binary magnesium diboride. Three different SiC powders were used, the average particle sizes were 200 nm, 30 nm, and 15 nm. The strands were heat treated for times ranging from 5 to 30 minutes at temperatures from 675 to 900. Strands with 200 nm size SiC additions had Hirr and Bc2 which maximized at 25.4 T and 29.7 T after heating at 800C for 30 minutes. The highest values were seen for a strand with 15 nm SiC heated at 725C for 30 minutes which had a Hirr of 29 T and a Bc2 higher than 33 T
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- 2004
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38. Irreversibility Field and Flux Pinning in MgB2 with and Without SiC Additions
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Sumption, M. D., Bhatia, M., Collings, E. W., Rhindfliesh, M., Tomsic, M., Hascicek, Y., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity - Abstract
Critical current density was measured at 4.2 K for MgB2 strands with and without SiC additions. In some cases measurements were performed on longer (1 m) samples wound on barrels, and these were compared to magnetic measurements. Most measurements were performed on short samples at higher fields (up to 18 T). It was found that in-situ processed strands with 10% SiC additions HT at 700-800C show improved Hr and Fp values as compared to control samples, with Hr increasing by 1.5 T. At 900C even larger improvements are seen, with Hr reaching 18 T and Fp values maximizing at 20 GN/m3., Comment: 15 pages, 1 table, six figs
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- 2004
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39. Effect of Nano Scale Fe Doping on Superconducting Properties of MgB2
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Dou, S. X., Soltanian, S., Zhao, Y., Getin, E., Chen, Z., and Horvat, J.
- Subjects
Condensed Matter - Superconductivity - Abstract
Iron is an important sheath material for fabrication of MgB2 wires. However, the effect of Fe doping on the superconducting properties of MgB2 remains controversial. In this work, we present results of nano-scale Fe particle doping in to MgB2. The Fe doping experiments were performed using both bulk and thin film form. It was found that Fe doping did not affect the lattice parameters of MgB2, as evidenced by the lack of change in the XRD peak positions for MgB2. Because of the high reactivity of nano-scale Fe particles, Fe doping is largely in the form of FeB at low doping level while Fe2B was detected at 10wt% doping by both XRD and TEM. There is no evidence for Fe substitution for Mg. The transition temperature decreased modestly with increasing Fe doping levels. The Jc(H) performance was severely depressed at above 3wt% doping level. The detrimental effect of nano-scale Fe doping on both Tc and Jc(H) is attributable to the grain decoupling as a result of magnetic scattering of Fe-containing dopants at grain boundaries.
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- 2004
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40. Comparative study of in situ and ex situ MgB2 films deposited by pulsed laser deposition
- Author
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Zhao, Y., Ionescu, M., Horvat, J., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity - Abstract
Two types of MgB2 films were prepared by pulsed laser deposition (PLD) with in situ and ex situ annealing processes respectively. Significant differences in properties between the two types of films were found. The ex situ MgB2 film has a Tc of 38.1K, while the in situ film has a depressed Tc of 34.5K. The resistivity at 40K for the in situ film is larger than that of the ex situ film by a factor of 6. The residual resistivity ratios (RRR) are 1.1 and 2.1 for the in situ and ex situ films respectively. The Jc-H curves of the in situ film show a much weaker field dependence than those of the ex situ film, attributable to stronger flux pinning in the in situ film. The small-grain feature and high oxygen level may be critical for the significant improvement of Jc in the in situ annealed MgB2 film., Comment: 6 pages, 6 figures
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- 2003
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41. Correlated vortex pinning in Si-nanoparticle doped MgB2
- Author
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Kusevic, I., Babic, E., Husnjak, O., Soltanian, S., Wang, X. L., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity ,Condensed Matter - Materials Science - Abstract
The magnetoresistivity and critical current density of well characterized Si-nanoparticle doped and undoped Cu-sheathed MgB$_{2}$ tapes have been measured at temperatures $T\geq 28$ K in magnetic fields $B\leq 0.9$ T. The irreversibility line $B_{irr}(T)$ for doped tape shows a stepwise variation with a kink around 0.3 T. Such $B_{irr}(T)$ variation is typical for high-temperature superconductors with columnar defects (a kink occurs near the matching field $% B_{\phi}$) and is very different from a smooth $B_{irr}(T)$ variation in undoped MgB$_{2}$ samples. The microstructure studies of nanoparticle doped MgB$_{2}$ samples show uniformly dispersed nanoprecipitates, which probably act as a correlated disorder. The observed difference between the field variations of the critical current density and pinning force density of the doped and undoped tape supports the above findings., Comment: 4 pages, 4 figures
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- 2003
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42. Si doping on MgB2 thin films by pulsed laser deposition
- Author
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Zhao, Y., Ionescu, M., Horvat, J., Li, A. H., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity - Abstract
A series of MgB2 thin films were fabricated by pulsed laser deposition (PLD), doped with various amounts of Si up to a level of 18wt%. Si was introduced into the PLD MgB2 films by sequential ablation of a stoichiometric MgB2 target and a Si target. The doped films were deposited at 250 C and annealed in situ at 685 C for 1min. Up to a Si doping level of ~11wt%, the superconducting transition temperature (Tc) of the film does not change significantly, as compared to the control, undoped film. The magnetic critical current density (Jc) of the film at 5K was increased by 50% for a Si doping level of ~3.5wt%, as compared to the control film. Also, the irreversibility field of Si-doped MgB2 films (Hirr) at low temperature is higher than for the undoped film., Comment: 7 pages, 7 figures; typos corrected in Figure 5
- Published
- 2003
43. Effect of carbon nanotube doping on critical current density of MgB2 superconductor
- Author
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Dou, S. X., Yeoh, W. K., Horvat, J., and Ionescu, M.
- Subjects
Condensed Matter - Superconductivity - Abstract
The effect of doping MgB2 with carbon nanotubes on transition temperature, lattice parameters, critical current density and flux pinning was studied for MgB2-xCx with x = 0, 0.05, 0.1, 0.2 and 0.3. The carbon substitution for B was found to enhance Jc in magnetic fields but depress Tc. The depression of Tc, which is caused by the carbon substitution for B, increases with increasing doping level, sintering temperature and duration. By controlling the extent of the substitution and addition of carbon nanotubes we can achieve the optimal improvement on critical current density and flux pinning in magnetic fields while maintaining the minimum reduction in Tc. Under these conditions, Jc was enhanced by two orders of magnitude at 8T and 5K and 7T and 10K. Jc was more than 10,000A/cm2 at 20K and 4T and 5K and 8.5T, respectively.
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- 2003
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44. Nanoscale-SiC doping for enhancing Jc and Hc2 in the Superconducting MgB2
- Author
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Dou, S. X., Braccini, V., Soltanian, S., Klie, R., Zhu, Y., Li, S., Wang, X. L., and Larbalestier, D.
- Subjects
Condensed Matter - Superconductivity - Abstract
The effect of nanoscale-SiC doping of MgB2 was investigated using transport and magnetic measurements. It was found that there is a clear correlation between the critical temperature Tc, the resistivity r, the residual resistivity ratio, RRR = R(300K)/R(40K), the irreversibility field H* and the alloying state in the samples. SiC-doping introduced many nano-scale precipitates, provoking an increase of r(40K) from 1 mW-cm (RRR = 15) for the clean limit sample to 300 mW-cm (RRR = 1.75) for the SiC-doped sample, leading to significant enhancement of Hc2 and H* with only minor effect on Tc. EELS analysis revealed a number of nano-scale impurity phases: Mg2Si, MgO, MgB4, BOx, SixByOz, BC and unreacted SiC in the doped sample. TEM study showed an extensive domain structure of 2-4nm domains induced by SiC doping. The Jc for the 10% nano-SiC doped sample increased substantially at all fields and temperatures compared to the undoped samples, due to the strong increase in Hc2 and H* produced by SiC doping.
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- 2003
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45. The origin of paramagnetic magnetization in field-cooled YBa2Cu3O7 films
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Luzhbin, D. A., Pan, A. V., Komashko, V. A., Flis, V. S., Pan, V. M., Dou, S. X., and Esquinazi, P.
- Subjects
Condensed Matter - Superconductivity - Abstract
Temperature dependences of the magnetic moment have been measured in YBa_2Cu_3O_{7-\delta} thin films over a wide magnetic field range (5 <= H <= 10^4 Oe). In these films a paramagnetic signal known as the paramagnetic Meissner effect has been observed. The experimental data in the films, which have strong pinning and high critical current densities (J_c ~ 2 \times 10^6 A/cm^2 at 77 K), are quantitatively shown to be highly consistent with the theoretical model proposed by Koshelev and Larkin [Phys. Rev. B 52, 13559 (1995)]. This finding indicates that the origin of the paramagnetic effect is ultimately associated with nucleation and inhomogeneous spatial redistribution of magnetic vortices in a sample which is cooled down in a magnetic field. It is also shown that the distribution of vortices is extremely sensitive to the interplay of film properties and the real experimental conditions of the measurements., Comment: RevTex, 8 figures
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- 2003
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46. On the sample size dependence of the critical current density in MgB$_2$ superconductors
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Qin, M. J., Keshavarzi, S., Soltanian, S., Wang, X. L., Liu, H. K., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity - Abstract
Sample size dependent critical current density has been observed in magnesium diboride superconductors. At high fields, larger samples provide higher critical current densities, while at low fields, larger samples give rise to lower critical current densities. The explanation for this surprising result is proposed in this study based on the electric field generated in the superconductors. The dependence of the current density on the sample size has been derived as a power law $j\propto R^{1/n}$ ($n$ is the $n$ factor characterizing $E-j$ curve $E=E_c(j/j_c)^n$). This dependence provides one with a new method to derive the $n$ factor and can also be used to determine the dependence of the activation energy on the current density., Comment: Revtex, 4 pages, 5 figures
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- 2003
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47. Effects of Fission-Fragment Damage on Vortex Dimensionality in Silver-sheathed Bi2Sr2Ca2Cu3Ox Tapes
- Author
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Marinaro, D., Horvat, J., Dou, S. X., Weinstein, R., and Gandini, A.
- Subjects
Condensed Matter - Superconductivity - Abstract
We report on the vortex dimensionality of uranium-doped Ag/Bi2223 tapes, before and after irradiation to a thermal-neutron fluence. The effective activation energies as a function of current density and applied field were calculated from dynamic magnetisation relaxation measurements. A dimensional crossover from a 3D elastic creep regime to 2D plastic creep was observed in the nonirradiated tape at an applied magnetic field Hcr = 0.37 T, with an associated change in the flux hop velocity and temperature dependence of the activation energy. After introduction of the fission-fragment damage by irradiation, a shift in the crossover to Hcr = 0.65 T was observed. These results indicate an enhancement of the c-axis vortex coherence by the introduced splayed columnar defects, explaining the greater pinning efficiency of the uranium-fission method in Bi2223 rather than the less anisotropic Y123. Conflicting results obtained for the irradiated tape in the absence of any temperature scaling of the activation energies demonstrate the importance of the inclusion of scaling in the magnetisation relaxation analysis.
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- 2003
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48. Uranium Doping and Thermal Neutron Irradiation Flux Pinning Effects in MgB2
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Silver, T., Horvat, J., Reinhard, M., Pei, Y., Keshavarzi, S., Munroe, P., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity - Abstract
The U/n method is a well-established means of improving flux pinning and critical current performance in cuprate superconductors. The method involves the doping of the superconductor with 235U followed by irradiation with thermal neutrons to promote fission. The resultant columnar damage tracks produced by the energetic fission products pin flux vortices and improve critical current performance in magnetic fields. No such improvement could be observed when the U/n method was applied to MgB2 superconductor. No fission tracks could be observed in TEM, even for samples that were irradiated at the highest fluence. Gamma-ray spectroscopy indicated that fission had occurred in the expected way.
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- 2003
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49. The effect of sample size on field dependence of Jc for MgB2 superconductor
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Horvat, J., Soltanian, S., Wang, X. L., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity - Abstract
A strong effect of sample size on magnetic Jc(H) was observed for bulk MgB2 when Jc is obtained directly from the critical state model. Thus obtained zero-field Jc (Jc0) decreases strongly with the sample size, attaining a constant value for the samples larger than a few millimetres. On the other hand, the irreversibility field (Hirr) defined at Jc = 100 A/cm2 increases with the sample size. The decrease of Jc0 is described in terms of voids in the bulk MgB2 samples and superconducting screening around the cells of superconducting material between these voids (35 micro-m), because of concentration of the current in the narrow bridges connecting the cells. For samples larger than a few millimetres, the value of magnetic Jc is in agreement with the transport Jc and it is restricted by the voids. The critical state model is not suitable for obtaining Jc for small bulk MgB2. The increase of Hirr with the sample size is an artefact of defining Hirr by the value of Jc at which an additional superconducting screening on 1mm scale dominates Dm.
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- 2003
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50. Effect of nano-carbon particle doping on the flux pinning properties of MgB2 superconductor
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Soltanian, S., Horvat, J., Wang, X. L., Munroe, P., and Dou, S. X.
- Subjects
Condensed Matter - Superconductivity - Abstract
Polycrystalline MgB2-xCx samples with x=0.05, 0.1, 0.2, 0.3, 0.4 nano-particle carbon powder were prepared using an in-situ reaction method under well controlled conditions to limit the extent of C substitution. The phases, lattice parameters, microstructures, superconductivity and flux pinning were characterized by XRD, TEM, and magnetic measurements. It was found that both the a-axis lattice parameter and the Tc decreased monotonically with increasing doping level. For the sample doped with the highest nominal composition of x=0.4 the Tc dropped only 2.7K. The nano-C-doped samples showed an improved field dependence of the Jc compared with the undoped sample over a wide temperature range. The enhancement by C-doping is similar to that of Si-doping but not as strong as for nano-SiC doped MgB2. X-ray diffraction results indicate that C reacted with Mg to form nano-size Mg2C3 and MgB2C2 particles. Nano-particle inclusions and substitution, both observed by transmission electron microscopy, are proposed to be responsible for the enhancement of flux pinning in high fields., Comment: 9 pages, 12 figures
- Published
- 2003
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