A giant magnetocaloric effect was found in MnAs, which undergoes a first-order ferromagnetic to paramagnetic transition at 318 K. The magnetic entropy change caused by a magnetic field of 5 T is as large as 30 J/K kg at the maximum value, which exceeds that of conventional magnetic refrigerant materials by a factor of 2–4. The adiabatic temperature change reaches 13 K in a field change of 5 T. The substitution of 10% Sb for As reduces the thermal hysteresis and lowers the Curie temperature to 280 K, while the giant magnetocaloric properties are retained.
The magnetocaloric effect of Mn3GaC, which shows an antiferromagnetic to ferromagnetic transition at 165 K has been investigated. In this compound, magnetocaloric effect obtained at the transition is opposite to that of ordinary ferromagnetic systems, namely, negative magnetocaloric effect. It was found that a large magnetic entropy change, ΔSmag, of 15 J/kg K is obtained under an applied field of 2 T. The adiabatic temperature change, ΔTad, reaches 5.4 K in a field change of 2 T. At higher magnetic fields, both ΔSmag and ΔTad retain a large value over wide temperature range, exhibiting characteristic temperature dependence of a trapezoidal shape. These features are attributed to a sharp first-order transition retained in high magnetic fields as well as small magnetocrystalline anisotropy.
The authors evaluated a nonenhanced magnetic resonance (MR) angiographic technique that allows separation of arteries from veins. In 15 healthy subjects, peripheral MR angiography was performed with readout flow-spoiled gradient pulses in electrocardiography-triggered three-dimensional half-Fourier fast spin-echo MR imaging. Appropriate flow-spoiled gradient pulses were measured and applied in the three-dimensional acquisition to differentiate arteries and veins in the peripheral vasculature. Subtraction of the diastolic bright-blood arteries from the systolic black-blood arteries allowed visualization of the arteries by cancelling the veins, which are constantly depicted as bright blood throughout the cardiac cycle. Stronger flow-spoiled gradient pulses improved the depiction of slow-flow arteries even in the distal foot and hand vessels.
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