19 research outputs found
Finite size effects with variable range exchange coupling in thin-film Pd/Fe/Pd trilayers
The magnetic properties of thin-film Pd/Fe/Pd trilayers in which an embedded
~1.5 A-thick ultrathin layer of Fe induces ferromagnetism in the surrounding Pd
have been investigated. The thickness of the ferromagnetic trilayer is
controlled by varying the thickness of the top Pd layer over a range from 8 A
to 56 A. As the thickness of the top Pd layer decreases, or equivalently as the
embedded Fe layer moves closer to the top surface, the saturated magnetization
normalized to area and the Curie temperature decrease whereas the coercivity
increases. These thickness-dependent observations for proximity-polarized
thin-film Pd are qualitatively consistent with finite size effects that are
well known for regular thin-film ferromagnets. The critical exponent of
the order parameter (magnetization) is found to approach the mean field value
of 0.5 as the thickness of the top Pd layer increases. The functional forms for
the thickness dependences, which are strongly modified by the nonuniform
exchange interaction in the polarized Pd, provide important new insights to
understanding nanomagnetism in two-dimensions.Comment: 14 pages, 5 figures, submitted to JMM
Pulmonary hemodynamic responses to in utero ventilation in very immature fetal sheep
<p>Abstract</p> <p>Background</p> <p>The onset of ventilation at birth decreases pulmonary vascular resistance (PVR) resulting in a large increase in pulmonary blood flow (PBF). As the large cross sectional area of the pulmonary vascular bed develops late in gestation, we have investigated whether the ventilation-induced increase in PBF is reduced in immature lungs.</p> <p>Methods</p> <p>Surgery was performed in fetal sheep at 105 d GA (n = 7; term ~147 d) to insert an endotracheal tube, which was connected to a neonatal ventilation circuit, and a transonic flow probe was placed around the left pulmonary artery. At 110 d GA, fetuses (n = 7) were ventilated <it>in utero </it>(IUV) for 12 hrs while continuous measurements of PBF were made, fetuses were allowed to develop <it>in utero </it>for a further 7 days following ventilation.</p> <p>Results</p> <p>PBF changes were highly variable between animals, increasing from 12.2 ± 6.6 mL/min to a maximum of 78.1 ± 23.1 mL/min in four fetuses after 10 minutes of ventilation. In the remaining three fetuses, little change in PBF was measured in response to IUV. The increases in PBF measured in responding fetuses were not sustained throughout the ventilation period and by 2 hrs of IUV had returned to pre-IUV control values.</p> <p>Discussion and conclusion</p> <p>Ventilation of very immature fetal sheep <it>in utero </it>increased PBF in 57% of fetuses but this increase was not sustained for more than 2 hrs, despite continuing ventilation. Immature lungs can increase PBF during ventilation, however, the present studies show these changes are transient and highly variable.</p