Enhanced critical current density of YBa2Cu3Ox films grown on Nd1/3Eu1/3Gd1/3Ba2Cu3Ox with nano-undulated surface morphology

We report a simple and easily controllable method where a nano-undulated surface morphology of Nd1/3Eu1/3Gd1/3Ba2Cu3Ox (NEG) films leads to a substantial increase in the critical current density in superconducting YBa2Cu3Ox (YBCO) films deposited by pulsed laser deposition on such NEG layers. The enhancement is observed over a wide range of fields and temperatures. Transmission electron microscopy shows that such YBCO films possess a high density of localized areas, typically 20 x 20 nm2 in size, where distortion of atomic planes give rotational (2 to 5 degrees) moire patterns. Their distribution is random and uniform, and expected to be the origin of the enhanced flux pinning. Magneto-optical imaging shows that these films have excellent macroscopic magnetic uniformity.Comment: 4 pages, 4 figure

Asymmetric nuclear matter in a Hartree-Fock approach to non-linear QHD

The Equation of State (EOS) for asymmetric nuclear matter is discussed starting from a phenomenological hadronic field theory of Serot-Walecka type including exchange terms. In a model with self interactions of the scalar sigma-meson we show that the Fock terms naturally lead to isospin effects in the nuclear EOS. These effects are quite large and dominate over the contribution due to isovector mesons. We obtain a potential symmetry term of "stiff" type, i.e. increasing with baryon density and an interesting behaviour of neutron/proton effective masses of relevance for transport properties of asymmetric dense matter.Comment: 12 pages (LATEX), 3 Postscript figures, revised versio

Fine structure in the α decay of 223U

Fine structure in the α decay of 223U was observed in the fusion-evaporation reaction 187Re(40Ar, p3n) by using fast digital pulse processing technique. Two α-decay branches of 223U feeding the ground state and 244 keV excited state of 219Th were identified by establishing the decay chain 223U →α1 219Th →α2 215Ra →α3 211Rn. The α-particle energy for the ground-state to ground-state transition of 223U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62−10+14 μs. Evolution of nuclear structure for N = 131 even-Z isotones from Po to U was discussed in the frameworks of nuclear mass and reduced α-decay width, a weakening octupole deformation in the ground state of 223U relative to its lighter isotones 219Ra and 221Th was suggested

How national policies facilitate low carbon city development: a China study

Low-carbon city development plays a critical role in the sustainable development of a country, especially to those new emerging economies such as China. The Chinese government recognizes the leading role of national policy system in facilitating the low-carbon city development. Meanwhile, positive effects are derived from the implementation of national policies. This study critically analyzed various policies promulgated during 2010–2019 by the Chinese government. A multi-dimensional framework is developed in this study to better understand the policies related to low carbon city development in China. These state-level policies are classified into six aspects: planning guidance, building energy conservation, industrial development regulation, energy industry development and energy mix, economic measures, and supervision measures. The evolution of these policies is examined in this study. Results show that national policies play a significant role in guiding low-carbon development of cities while the practicability of these national policies is improved. In addition, the development of low carbon city clusters is actively promoted by the Chinese government and linked to other strategic initiatives such as “The Belt and Road”. These findings help to better understand the national policy landscape of low carbon city development in China, as well as providing useful references to the policy making in other countries.Zhen-Yu Zhao, Lei Gao, Jian Zu

Suppressing σ phase formation by rapid solidification to prevent embrittlement in a low-cost aged medium-entropy alloy

Developing cost-effective high- and medium-entropy alloys (HEAs/MEAs) is essential to promote their broad industrial applications. A newly developed low-cost Fe45Cr25Ni10Mn15Al4C1 (at.%) MEA shows excellent compressive strength and ductility, but it is highly susceptible to drastic embrittlement when a substantial amount of σ phase is presented. The study herein explored the utilization of rapid solidification (RS) with high cooling rate to produce the MEA and compared it with hot-rolled (HR) sample. Two major phases, face-centered cubic (FCC) and body-centered cubic (BCC), exist in both RS and HR samples with high-density NiAl-rich B2 nano-precipitates inside BCC phase. RS sample contains two regions with different microstructural morphologies where central zone undergoes larger thermal gradient and cooling rate and exhibits acicular FCC phase in coarse BCC matrix, while ring zone possesses alternating dendritic structures. Uniform crystal orientations and decreased chemical segregation are additionally found in RS sample. The transformation from BCC to σ phase in RS sample is significantly suppressed, which avoids the embrittlement. This is attributed to several factors including the reduced grain boundaries, decreased dislocation stored energy, and lower Cr content in BCC phase of RS sample. These factors effectively prolong the incubation time of σ phase nucleation. In addition, diffusion is clearly involved as σ phase forms and stabilizes, identified by the huge variations in Ni and Cr contents of B2 nano-precipitates within σ phase. The present study may open a new pathway towards harnessing the formation of σ phase to develop strong and ductile HEAs/MEAs at low cost