Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 22 of 22
Full-Text Articles in Engineering
Order-Disorder Transition In Bi2.1sr1.9cacu2o8 + Delta Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Order-Disorder Transition In Bi2.1sr1.9cacu2o8 + Delta Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Hua Kun Liu
The magnetic field Hdis(T) where an order-disorder transition of the vortex lattice in high-Tc superconductors occurs, is investigated by measurements of the magnetization M(H) in Bi2.1Sr1.9CaCu2O8 + delta (Bi2212) single crystals doped with iron and lead. Comparative studies are made of the temperature dependences of the field Hpeak(T), where the second peak occurs in |M(H)|, and the fields Hmin(T), and Hinfl(T) where a minimum and an inflection point occur at the low-field side of this peak. It is proposed that Hdis(T) lies close to Hinfl. In Bi2.1Sr1.9Ca1.0(Cu1–yFey)2O8 + delta single crystals with Fe concentration y = 0, 0.005, 0.016, and …
Synthesis Of Nonstoichiometric Amorphous Mg-Based Alloy Electrodes By Mechanical Milling, L. Sun, Hua-Kun Liu, D. H. Bradhurst, S. X. Dou
Synthesis Of Nonstoichiometric Amorphous Mg-Based Alloy Electrodes By Mechanical Milling, L. Sun, Hua-Kun Liu, D. H. Bradhurst, S. X. Dou
Hua Kun Liu
Nonstoichiometric amorphous Mg-Ni and Mg-Ni-V alloys were synthesized by mechanical milling the crystalline Mg2Ni alloy with Ni and/or V powders. All the nonstoichiometric amorphous Mg-based alloys result in Mg-based alloy electrodes with very high discharge capacities by comparison with crystalline Mg2Ni alloys. The results indicate that nonstoichiometric amorphous Mg-based alloys can be obtained either by increasing the Ni content, adding a range of other elements, or both, using a mechanical milling method. The nonstoichiometric Mg-based alloy electrodes studied have shown improved initial discharge capacities compared with the stoichiometric amorphous MgNi alloy. These results describe a method of achieving better Mg-based …
Sample-Size Dependence Of The Magnetic Critical Current Density In Mgb2 Superconductors, M. J. Qin, S. Keshavarzi, Saeid Soltanian, Xiaolin Wang, Hua-Kun Liu, S. X. Dou
Sample-Size Dependence Of The Magnetic Critical Current Density In Mgb2 Superconductors, M. J. Qin, S. Keshavarzi, Saeid Soltanian, Xiaolin Wang, Hua-Kun Liu, S. X. Dou
Hua Kun Liu
Sample size dependent magnetic 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}R1/n @n is the n factor characterizing E2j curve E 5Ec( j/ jc)n]. This dependence provides one with a method to derive the n factor and …
Study Of Oxygen Incorporation In Pld Mgb2 Films By Rutherford Backscattering Spectroscopy, Y. Zhao, M. Ionescu, S X. Dou, Hua-Kun Liu
Study Of Oxygen Incorporation In Pld Mgb2 Films By Rutherford Backscattering Spectroscopy, Y. Zhao, M. Ionescu, S X. Dou, Hua-Kun Liu
Hua Kun Liu
The Rutherford backscattering (RBS) method has been employed to study the incorporation of oxygen into MgB2 films during their fabrication by pulsed-laser deposition (PLD). A series of MgB2 thin film samples were analyzed, including two films produced in situ on Al2O3-c substrates (with higher Tc and lower Tc) with an on-axis geometry, one film produced in situ with an off-axis geometry, and one film produced ex situ, with a bulk-like Tc. The amount of oxygen detected by RBS, which is stable in the form of MgO, appears to be correlated with the Tc of the films, the higher the Tc …
Transport Critical Current Density In Fe-Sheathed Nano-Sic Doped Mgb/Sub 2/ Wires, S X. Dou, J. Horvat, Saeid Soltanian, Xiaolin Wang, M. J. Qin, S. H. Zhou, Hua-Kun Liu, P. G. Munroe
Transport Critical Current Density In Fe-Sheathed Nano-Sic Doped Mgb/Sub 2/ Wires, S X. Dou, J. Horvat, Saeid Soltanian, Xiaolin Wang, M. J. Qin, S. H. Zhou, Hua-Kun Liu, P. G. Munroe
Hua Kun Liu
The nano-SiC doped MgB/sub 2//Fe wires were fabricated using a powder-in-tube method and an in-situ reaction process. The depression of T/sub c/ with increasing SiC doping level remained rather small due to the counterbalanced effect of Si and C co-doping. The high level SiC co-doping allowed creation of the intra-grain defects and nano-inclusions, which act as effective pinning centers, resulting in a substantial enhancement in the J/sub c/(H) performance. The transport J/sub c/ for all the wires is comparable to the magnetic J/sub c/ at higher fields despite the low density of the samples and percolative nature of current. The …
Dependence Of The Flux-Creep Activation Energy On Current Density And Magnetic Field For The Mgb2 Superconductor, M. J. Qin, Xiaolin Wang, Saeid Soltanian, Aihua Li, Hua-Kun Liu, S. X. Dou
Dependence Of The Flux-Creep Activation Energy On Current Density And Magnetic Field For The Mgb2 Superconductor, M. J. Qin, Xiaolin Wang, Saeid Soltanian, Aihua Li, Hua-Kun Liu, S. X. Dou
Hua Kun Liu
Systematic ac susceptibility measurements have been performed on a MgB2 bulk sample. We demonstrate that the flux creep activation energy is a nonlinear function of the current density U(j)∝j-0.2, indicating a nonlogarithmic relaxation of the current density in this material. The dependence of the activation energy on the magnetic field is determined to be a power law U(B)∝B-1.33, showing a steep decline in the activation energy with the magnetic field, which accounts for the steep drop in the critical current density with magnetic field that is observed in MgB2. The irreversibility field is also found to be rather low, therefore, …
Silicon/Disordered Carbon Nanocomposites For Lithium-Ion Battery Anodes, Z. P. Guo, E. Milin, J. Z. Wang, Jun Chen, Hua-Kun Liu
Silicon/Disordered Carbon Nanocomposites For Lithium-Ion Battery Anodes, Z. P. Guo, E. Milin, J. Z. Wang, Jun Chen, Hua-Kun Liu
Hua Kun Liu
Silicon/disordered carbon Si-DC nanocomposites have been synthesized by high-energy ballmilling of Si-sucrose and silicon-polyvinyl alcohol followed by pyrolysis under argon flow. The exact disordered carbon content in the as-prepared Si-DC nanocomposites was determined by thermogravimetric analysis for the first time. Based on the thermogravimetric analysis, X-ray diffraction, Raman, and cyclic voltammetric results, we believe that carbon distribution on the Si particles in Si-DC nanocomposite using PVA as the carbon source is more uniform and has higher efficiency than that using sucrose as the carbon source, under the same preparation conditions. The carbon content and the starting polymers significantly affect the …
Magneto-Optical Images Of Ag/Bi-2223 Tapes Processed By Flat Rolling, “Sandwich” Rolling And Pressing, Hua-Kun Liu, A. Polyanskii, W. M. Chen, Y. C. Guo, S. X. Dou, M. Apperley
Magneto-Optical Images Of Ag/Bi-2223 Tapes Processed By Flat Rolling, “Sandwich” Rolling And Pressing, Hua-Kun Liu, A. Polyanskii, W. M. Chen, Y. C. Guo, S. X. Dou, M. Apperley
Hua Kun Liu
Magneto-optical imaging (MOI) has been used for study Ag/Bi-2223 tapes processed using flat rolling, “sandwich” rolling, and pressing methods for the intermediate mechanical deformation in powder-in-tube process. The results show that not only the density of the microcracks but also their distribution affect Jc. Rolled tapes have a higher density of microcracks than pressed tapes. Although the flat rolled tape and “sandwich” rolled tape have the same level density of microcracks at the same reduction, the cracks in the former are more in the transverse direction than in the latter. In all three cases, Jc reaches a maximum value at …
Fission Converter And Metal–Oxide–Semiconductor Field Effect Transistor Study Of Thermal Neutron Flux Distribution In An Epithermal Neutron Therapy Beam, G. I. Kaplan, Anatoly B. Rosenfeld, B. J. Allen, J. A. Coderre, H. B. Liu
Fission Converter And Metal–Oxide–Semiconductor Field Effect Transistor Study Of Thermal Neutron Flux Distribution In An Epithermal Neutron Therapy Beam, G. I. Kaplan, Anatoly B. Rosenfeld, B. J. Allen, J. A. Coderre, H. B. Liu
Hua Kun Liu
The depth distribution of the thermal neutron flux is a major factor in boron neutron capture therapy (BNCT) in determining the efficiency of cell sterilization. In this paper the fission detector method is developed and applied to measure the in-phantom thermal neutron flux depth distribution. Advantages of the fission detector include small size, direct measurement of thermal neutron flux in a mixed radiation field of BNCT beam, self-calibration, and the possibility of on-line measurement. The measurements were performed at epithermal a BNCT facility. The experimental results were compared with the thermal neutron flux calculated by the Monte Carlo method and …
Magnetic Hysteresis And Relaxation In Bi2212 Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, G. D. Gu, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Magnetic Hysteresis And Relaxation In Bi2212 Single Crystals Doped With Fe And Pb, K. K. Uprety, J. Horvat, Xiaolin Wang, G. D. Gu, M. Ionescu, Hua-Kun Liu, S. X. Dou, E. H. Brandt
Hua Kun Liu
Magnetic hysteresis and magnetic relaxation measurements have been performed to study vortex pinning behaviors for pure, Fe doped and heavily Pb doped Bi2212 single crystals. Unlike pure and Fe doped Bi2212 crystals, heavily Pb doped crystal showed strong vortex pinning behavior. We interpret the strong pinning in heavily Pb doped Bi2212 single crystals as arising from the improved Josephson coupling in Bi2212 single crystal after heavy Pb doping. In heavily Pb doped single Bi2212 crystals, H/sub dis/(T) was observed to decrease with increasing T. Here, H/sub dis/(T) is an order-disorder field that separates a weakly elastically disordered vortex lattice from …
Anomalous Magnetization Peak Effect In Spiral-Grown Bi2sr2cacu2oy Crystals, Xiaolin Wang, J. Horvat, Hua-Kun Liu, J. N. Li, S. X. Dou
Anomalous Magnetization Peak Effect In Spiral-Grown Bi2sr2cacu2oy Crystals, Xiaolin Wang, J. Horvat, Hua-Kun Liu, J. N. Li, S. X. Dou
Hua Kun Liu
Magnetic hysteresis loops were measured on spiral-grown Bi2Sr2CaCu2Oy (Bi-2212) crystals. An anomalous peak effect at a magnetic field of 1000–2000 Oe was observed both in high-Tc (86 K) and oxygen underdoped (Tc=76 K) spiral-grown crystals between 20 and 40 K. The peak effect was observed to be stronger than that induced by oxygen vacancies, defect dislocation networks reported in Bi-2212 crystals. Further, the anomalous peak almost completely disappeared after removing growth spiral patterns from the crystal surface. Edge barriers associated with the growth spirals are suggested to be responsible for the strong peak effect for the spiral-grown Bi-2212 crystals and …
Electro-Oxidation Of Ethanol On Pt-Wo3/C Electrocatalyst, D. Y. Zhang, Z. F. Ma, G. X. Wang, Konstantin Konstantinov, X. X. Yuan, Hua-Kun Liu
Electro-Oxidation Of Ethanol On Pt-Wo3/C Electrocatalyst, D. Y. Zhang, Z. F. Ma, G. X. Wang, Konstantin Konstantinov, X. X. Yuan, Hua-Kun Liu
Hua Kun Liu
Ptx-WO3/C electrocatalysts were prepared by microwave colloid-reduction method. Transmission electron microscopy examination showed uniform dispersion of platinum with particle sizes less than 5 nm. Structures of the Ptx-WO3/C electrocatalysts were characterized by X-ray diffraction and energy dispersive spectroscopy, the electrochemical characteristics and electro-oxidation of electro-oxidation of ethanol on the Ptx-WO3/C electrocatalysts were also studied by cyclic voltammetry, linear sweep, and chronoamperometry. The results show that the Ptx-WO3/C electrocatalysts have higher catalytic activity to ethanol electrooxidation than the commercial Pt/C catalysts; perhaps caused by the “hydrogen spill-over effect.” The reaction mechanisms of the ethanol electro-oxidation on the Ptx-WO3/C were inferred according …
Microstructure Observations Of Ag And Ag-Alloy Sheathed Bi2223 Tapes, Hua-Kun Liu, R. Zeng
Microstructure Observations Of Ag And Ag-Alloy Sheathed Bi2223 Tapes, Hua-Kun Liu, R. Zeng
Hua Kun Liu
Abstract—37 filament Bi2223 tapes with different configurations of Ag, AgAu7wt% AgSb0.6wt% and AgMg0.2wt% as the precursor and restack sheaths were fabricated using commercial Bi2223 precursor material and powder-in-tube techniques. Short length samples were heat treated at a temperature in the range of 832 C to 846 C for the first stage (HT 1), followed by a second stage (HT 2) at 825 C for 40 h and slow cooled to 785 C. An intermediate roll pass was performed between the heat treatment stages. The critical current (Ic) of the tapes was measured at 77 K in self-field and in fields …
Magnetoresistance And V-I Curves Of Ag-Sheathed (Bi,Pb)2sr2ca2cu3o10+Y Tape, E. Babic, I. Kusevic, S X. Dou, Hua-Kun Liu, Q. Y. Hu
Magnetoresistance And V-I Curves Of Ag-Sheathed (Bi,Pb)2sr2ca2cu3o10+Y Tape, E. Babic, I. Kusevic, S X. Dou, Hua-Kun Liu, Q. Y. Hu
Hua Kun Liu
The magnetoresistance and the V-I curves (I>Ic) of a well-characterized Ag-clad (Bi,Pb)2Sr2Ca2Cu3O10+y tape (BPSCCO) with Jc(77 K, B=0)=10 kA/cm2 have been analyzed in the temperature (T) range 80–110 K and magnetic field (B) up to 60 mT. The results obtained after the correction for the parallel conduction through the Ag sheathing and BPSCCO core are similar to those for corresponding single crystals and the epitaxial thin films. The effective activation energy for the flux creep U0 is larger than those for the single crystals and thin films of Bi-Sr-Ca-Cu-O (BSCCO) compound. The variations of the differential resistance Rf (deduced …
Characterization Of Thermal Conductivity And Mechanical Properties Of Ag-Alloy Sheathed Bi(Pb)-Sr-Ca-Cu-O Superconductor Tape, S. H. Jang, J. H. Lim, J. K. Kim, B. K. Ji, J. Jo, W. Nah, J. S. Volf, Hua-Kun Liu, M. Apperley
Characterization Of Thermal Conductivity And Mechanical Properties Of Ag-Alloy Sheathed Bi(Pb)-Sr-Ca-Cu-O Superconductor Tape, S. H. Jang, J. H. Lim, J. K. Kim, B. K. Ji, J. Jo, W. Nah, J. S. Volf, Hua-Kun Liu, M. Apperley
Hua Kun Liu
We evaluated the effect of alloying additions to Ag on thermal conductivity and mechanical properties of Ag-alloy sheathed Bi-2223 (BSCCO) superconductor tape. The tapes were made with combinations of Ag alloys such as Ag-Mg, Ag-Sb, and Ag-Au for inner and outer sheath. Thermal conductivity of the tapes was evaluated by using thermal integral method at 10-120 K. It was observed that the addition of alloys reduced remarkably thermal conductivity and improved mechanical strength. The thermal conductivity for Ag-Mg, Ag-Sb, and Ag-Au at 40 K was measured to be 411.4, 142.3, and 109.7 W/(m/spl middot/K), respectively, which is approximately 2 to …
Third Harmonics Due To Surface Barrier In High-Temperature Superconductor, X. B. Xu, L. Zhang, X. Leng, Shichao Ding, Hua-Kun Liu, Xiaolin Wang, S. X. Dou, Z. W. Lin, J. G. Zhu
Third Harmonics Due To Surface Barrier In High-Temperature Superconductor, X. B. Xu, L. Zhang, X. Leng, Shichao Ding, Hua-Kun Liu, Xiaolin Wang, S. X. Dou, Z. W. Lin, J. G. Zhu
Hua Kun Liu
The influence of surface barrier on the third harmonics ac susceptibility (chi3) is studied numerically. The surface barrier is described by a critical current density in surfaces which are higher than the inside one. The model can act as the critical state one, the flux creep one, or the flux flow one when temperature (or field) changes. The numerical results based on the model are more close to the popular experimental data probing the harmonics as a function of temperature (or field). Besides, the surface barrier will lead to new peaks in the real and imaginary parts of the third …
Tungsten Disulfide Nanotubes For Lithium Storage, G. X. Wang, S. Bewlay, J. Yao, Hua-Kun Liu, S. X. Dou
Tungsten Disulfide Nanotubes For Lithium Storage, G. X. Wang, S. Bewlay, J. Yao, Hua-Kun Liu, S. X. Dou
Hua Kun Liu
WS2 nanotubes were synthesized by sintering amorphous WS3 at high temperature under flowing hydrogen. High-resolution transmission electron microscopy observation revealed that the as-prepared WS2 nanotubes have an open end with an inner hollow core of about 4.6 nm. We studied the lithium intercalation behavior of WS2 nanotubes. The WS2 nanotubes demonstrated a stable cyclability in a wide voltage range ~0.1-3.1 V vs. Li/Li1). The nanotubes could provide a new class of electrode materials for lithium-ion batteries.
Synthesis And Characterization Of One-Dimensional Cdse Nanostructures, G. X. Wang, M. S. Park, Hua-Kun Liu, D. Wexler, Jun Chen
Synthesis And Characterization Of One-Dimensional Cdse Nanostructures, G. X. Wang, M. S. Park, Hua-Kun Liu, D. Wexler, Jun Chen
Hua Kun Liu
No abstract provided.
Electrochemical Performance Of Co3o4–C Composite Anode Materials, Scott A. Needham, G. X. Wang, Konstantin Konstantinov, Y. Tournayre, Z. Lao, Hua-Kun Liu
Electrochemical Performance Of Co3o4–C Composite Anode Materials, Scott A. Needham, G. X. Wang, Konstantin Konstantinov, Y. Tournayre, Z. Lao, Hua-Kun Liu
Hua Kun Liu
Co3O4–C composite powder has been synthesized via spray pyrolysis of cobalt nitrate-sugar solution at 600°C and assessed for application as anode materials in Li-ion batteries. Microstructural characterization by scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy confirm an even distribution of carbon throughout particles, as well as the presence of a carbon-based surface sheath surrounding Co3O4–C particle agglomerates. Charge-discharge cycling of half-cells indicates a stable reversible discharge capacity above 800 mAh g−1. Equivalent circuit modeling of Nyquist plots show the Co3O4–C electrode has significant kinetic advantages over non-composite transition metal oxide electrodes.
Superconductivity, Critical Current Density, And Flux Pinning In Mgb2–X(Sic)X/2 Superconductor After Sic Nanoparticle Doping, S X. Dou, A. V. Pan, S. Zhou, M. Ionescu, Xiaolin Wang, J. Horvat, Hua-Kun Liu, P. R. Munroe
Superconductivity, Critical Current Density, And Flux Pinning In Mgb2–X(Sic)X/2 Superconductor After Sic Nanoparticle Doping, S X. Dou, A. V. Pan, S. Zhou, M. Ionescu, Xiaolin Wang, J. Horvat, Hua-Kun Liu, P. R. Munroe
Hua Kun Liu
We investigated the effect of SiC nanoparticle doping on the crystal lattice structure, critical temperature Tc, critical current density Jc, and flux pinning in MgB2 superconductor. A series of MgB2–x(SiC)x/2 samples with x = 0–1.0 were fabricated using an in situ reaction process. The contraction of the lattice and depression of Tc with increasing SiC doping level remained rather small most likely due to the counterbalancing effect of Si and C co-doping. The high level Si and C co-doping allowed the creation of intragrain defects and highly dispersed nanoinclusions within the grains which can act as effective pinning centers for …
Intergranular And Intragranular Critical Currents In Silver-Sheathed Pb-Bi-Sr-Ca-Cu-O Tapes, K. Muller, C. Andrikidis, Hua-Kun Liu, S. X. Dou
Intergranular And Intragranular Critical Currents In Silver-Sheathed Pb-Bi-Sr-Ca-Cu-O Tapes, K. Muller, C. Andrikidis, Hua-Kun Liu, S. X. Dou
Hua Kun Liu
The role of the intergranular and intragranular critical current densities in silver-sheathed Pb-Bi-Sr-Ca-Cu-O tapes is investigated by means of magnetic-moment measurements in perpendicular field at different temperatures using a superconducting quantum interference device magnetometer. We find that low-field magnetic-moment loops are mainly caused by the intergranular (transport) critical current density JcJ but that in high fields the contribution from the intragranular critical current density JcG becomes significant. The low-field data can be described well in terms of a critical-state model for a thin strip of a homogeneous type-II superconductor in a perpendicular field where JcJ flows over the entire tape. …
Characterization Of Nanocrystalline Si-Mcmb Composite Anode Materials, G. X. Wang, J. Yao, Hua-Kun Liu
Characterization Of Nanocrystalline Si-Mcmb Composite Anode Materials, G. X. Wang, J. Yao, Hua-Kun Liu
Hua Kun Liu
Nanocrystalline Si-mesocarbon microbeads ~MCMB! composite anode materials were prepared by ballmilling. Scanning electron microscopic observation showed that the spherical shape of MCMB particles can be retained via moderate ballmilling. Ballmilling conditions have an impact on the capacity and cyclability of nanocrystalline Si-MCMB composites. The optimized Si-MCMB composite anode demonstrated a reversible capacity of 1066 mAh/g with good cyclability. A reaction model has been proposed to explain the reaction mechanisms of lithium insertion and extraction in the Si-MCMB electrode.