432 research outputs found
Effect of aromatic hydrocarbon addition on in situ powder-in-tube processed MgB2 tapes
We fabricated in situ powder-in-tube processed MgB2/Fe tapes using aromatic
hydrocarbon of benzene, naphthalene, and thiophene as additives, and
investigated the superconducting properties. We found that these aromatic
hydrocarbons were very effective for increasing the Jc values. The Jc values of
20mol% benzene-added tapes reached 130A/mm2 at 4.2K and 10T. This value was
almost comparable to that of 10mol% SiC-added tapes and about four times higher
than that of tapes with no additions. Microstructure analyses suggest that this
Jc enhancement is due to both the substitution of carbon for boron in MgB2 and
the smaller MgB2 grain size.Comment: 6 pages, 4 figure
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
Strain Effect in MgB2/Stainless Steel Superconducting Tape
The influence of mechanical strain on the critical current (Ic) is
investigated for MgB2/stainless steel (SUS316) superconducting tapes. The tapes
are fabricated by using 'powder in tube' method and deformation process without
any heat treatment. The tensile axial strain along tape length is successfully
induced to the sample by using a U-shape holder made of stainless steel
(SUS304). Two samples are examined at 4.2 K in 5 T (B is applied perpendicular
to the tape surface). While the initial Ic at zero external strain state (Ic0)
varies (30.4 and 33.3 A), normalized Ic (Ic/Ic0) vs. external strain relations
fall on the same curve. Linear increase of Ic is observed from zero external
strain state to 0.5% strain (107% of Ic0). Rapid and large degradation occurs
at the strain exceeding 0.4-0.5%. High durability against stress can be
expected for MgB2/stainless steel superconducting tapes.Comment: 3 pages including 2 figures, submitted to Physica
Superconducting Properties of MgB2 Bulk Materials Prepared by High Pressure Sintering
High-density bulk materials of a newly discovered 40K intermetallic MgB2
superconductor were prepared by high pressure sintering. Superconducting
transition with the onset temperature of 39K was confirmed by both magnetic and
resistive measurements. Magnetization versus field (M-H) curve shows the
behavior of a typical Type II superconductor and the lower critical field
Hc1(0) estimated from M-H curve is 0.032T. The bulk sample shows good
connection between grains and critical current density Jc estimated from the
magnetization hysteresis using sample size was 2x104A/cm2 at 20K and 1T. Upper
critical field Hc2(0) determined by extrapolating the onset of resistive
transition and assuming a dirty limit is 18T.Comment: 3Pages PD
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
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