492 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
Spin Squeezing via One-Axis Twisting with Coherent Light
We propose a new method of spin squeezing of atomic spin, based on the
interactions between atoms and off-resonant light which are known as
paramagnetic Faraday rotation and fictitious magnetic field of light. Since the
projection process, squeezed light, or special interactions among the atoms are
not required in this method, it can be widely applied to many systems. The
attainable range of the squeezing parameter is S^{-2/5}, where S is the total
spin, which is limited by additional fluctuations imposed by coherent light and
the spherical nature of the spin distribution.Comment: 4 pages,6 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
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
Fictitious Magnetic Resonance by Quasi-Electrostatic Field
We propose a new kind of spin manipulation method using a {\it fictitious}
magnetic field generated by a quasi-electrostatic field. The method can be
applicable to every atom with electron spins and has distinct advantages of
small photon scattering rate and local addressability. By using a
laser as a quasi-electrostatic field, we have experimentally demonstrated the
proposed method by observing the Rabi-oscillation of the ground state hyperfine
spin F=1 of the cold atoms and the Bose-Einstein condensate.Comment: 5 pages, 5 figure
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