361 research outputs found
Fabrication of high performance MgB2 wires by an internal Mg diffusion process
We succeeded in the fabrication of high-Jc MgB2/Fe wires applying the
internal Mg diffusion (IMD) process with pure Mg core and SiC addition. A pure
Mg rod with 2 mm diameter was placed at the center of a Fe tube, and the space
between Mg and Fe tube was filled with B powder or the powder mixture of
B-(5mol%)SiC. The composite was cold worked into 1.2mm diameter wire and
finally heat treated at temperatures above the melting point of Mg(~650oC).
During the heat treatment liquid Mg infiltrated into B layer and reacted with B
to form MgB2. X-ray diffraction analysis indicated that the major phase in the
reacted layer is MgB2. SEM analysis shows that the density of MgB2 layer is
higher than that of usual powder-in-tube(PIT) processed wires. The wires with
5mol% SiC addition heat treated at 670oC showed Jc values higher than 105A/cm2
in 8T and 41,000A/cm2 in 10T at 4.2K. These values are much higher than those
of usual PIT processed wires even compared to the ones with SiC addition.
Higher density of MgB2 layer obtained by the diffusion reaction is the major
cause of this excellent Jc values.Comment: 7page, 6figure
High transport critical current density obtained for Powder-In-Tube-processed MgB2 tapes and wires using stainless steel and Cu-Ni tubes
MgB2 tapes and wires were fabricated by the Powder-In-Tube method. Stainless
steel and Cu-Ni tubes were used as sheath materials, and no heat treatment was
applied. The tapes made of stainless steel showed transport critical current
density Jc of about 10,000A/cm2 at 4.2K and 5T. A high Jc of about 300,000A/cm2
was obtained by extrapolating the Jc-B curves to zero field.
Multifilamentary(7-core) MgB2 wire was successfully fabricated using Cu-Ni
tubes. For both tapes and wires the grain connectivity of MgB2 was as good as a
high-pressure sintered bulk sample. However, the Jc of the Cu-Ni sheathed wire
was lower than the stainless steel sheathed tape due to the lower packing
density of MgB2.Comment: 4 pages, 3 figure
Spatial reasoning skills about 2D representations of 3D geometrical shapes in grades 4 to 9
This is the final version. Available on open access from the Mathematics Education Research Group of Australasia via the DOI in this recordGiven the important role played by students’ spatial reasoning skills, in this paper we analyse how students use these skills to solve problems involving 2D representations of 3D geometrical shapes. Using data from in total 1357 grades 4 to 9 students, we examine how they visualise shapes in the given diagrams and make use of properties of shapes to reason. We found that using either spatial visualisation or property-based spatial analytic reasoning is not enough for the problems that required more than one step of reasoning, but also that these two skills have to be harmonised by domain-specific knowledge in order to overcome the perceptual appearance (or “look”) of the given diagram. We argue that more opportunities might be given to both primary and secondary school students in which they can exercise not only their spatial reasoning skills but also consolidate and use their existing domain-specific knowledge of geometry for productive reasoning in geometry
- …