In this study, a new cavity form filled under a constant magnetic field by Ag/MgO/H2O nanofluids and porous media consistent with natural convection and total entropy is examined. The nanofluid flow is considered to be laminar and incompressible, while the advection inertia effect in the porous layer is taken into account by adopting the Darcy–Forchheimer model. The problem is explained in the dimensionless form of the governing equations and solved by the finite element method. The results of the values of Darcy (Da), Hartmann (Ha) and Rayleigh (Ra) numbers, porosity (εp), and the properties of solid volume fraction (ϕ) and flow fields were studied. The findings show that with each improvement in the Ha number, the heat transfer rate becomes more limited, and thus the magnetic field can be used as an outstanding heat transfer controller.

Domain phases in ultrathin Fe/Ni/W(110) films with perpendicular anisotropy have been studied using the ac magnetic susceptibility. Dynamics on time scales of minutes to hours were probed by quenching the system from high temperature to the stripe phase region, and varying the constant rate of temperature increase as the susceptibility traces were measured. The entire susceptibility peak is observed to relax slowly along the temperature axis, with the peak temperature increasing as the rate of heating is decreased. This is precisely opposite to what would happen if this slow relaxation was driven by changes in the domain density within the stripe phase. The data are instead consistent with a simple model for the removal of a significant density of pattern defects and curvature trapped in the quench from high temperature. A quantitative analysis confirms that the relaxation dynamics are consistent with the mesoscopic rearrangement of domains required to remove pattern defects, and that the experiment constitutes a "dynamical" observation of the phase transition from a high temperature, positionally disordered domain phase to the low temperature, ordered stripe phase.

In the mixture of lipids and proteins which comprise pulmonary surfactant, the dominant protein by mass is surfactant protein A (SP-A), a hydrophilic glycoprotein. SP-A forms octadecamers that interact with phospholipid bilayer surfaces in the presence of calcium. Deuterium NMR was used to characterize the perturbation by SP-A, in the presence of 5 mM Ca(2+), of dipalmitoyl phosphatidylcholine (DPPC) properties in DPPC/egg-PG (7:3) bilayers. Effects of SP-A were uniformly distributed over the observed DPPC population. SP-A reduced DPPC chain orientational order significantly in the gel phase but only slightly in the liquid-crystalline phase. Quadrupole echo decay times for DPPC chain deuterons were sensitive to SP-A in the liquid-crystalline mixture but not in the gel phase. SP-A reduced quadrupole splittings of DPPC choline beta-deuterons but had little effect on choline alpha-deuteron splittings. The observed effects of SP-A on DPPC/egg-PG bilayer properties differ from those of the hydrophobic surfactant proteins SP-B and SP-C. This is consistent with the expectation that SP-A interacts primarily at bilayer surfaces.

Measurements of the ac magnetic susceptibility of perpendicularly magnetized Fe/2 ML Ni/W(110) ultrathin films show a clear signature of the dynamics of domain growth and domain density changes in the striped domain pattern that this system supports. The susceptibility peak measured at different constant heating rates in the range 0.20 K/s ≤ R ≤ 0.70 K/s shifts to higher temperature as the heating rate is increased. Analysis using a relaxation model demonstrates quantitatively that the dynamics is driven by a non-equilibrium domain density at (nearly) zero field (i.e. by dipole interactions), and that the temperature shift is due to a response time determined by the pinning of local domain wall segments by structural defects. The fundamental time scale for relaxation of the domain density driven by dipole interactions is of order 10 5 times slower than the fundamental time scale for an individual Barkhausen step driven by an applied field. The increase in the fundamental time scale reflects the relative size of dipole and Zeeman energies, and the need for the correlated motion of the many local domain wall segments required to affect domain growth.PACS numbers:

Two dimensional magnetic films with perpendicular magnetization spontaneously form magnetic domain patterns that evolve or undergo symmetry transformations as a function of temperature. When the system is driven from equilibrium by a rapid change in temperature, topological pattern defects are the elementary pattern excitations that affect this evolution. An elastic continuum model is adapted to describe how a metastable population of topological defects alters the domain density and the magnetic susceptibility of the "stripe" magnetic domain pattern. Temporal changes in the susceptibility are interpreted using a dynamical equation describing the defect population. Recent experiments provide a quantitative verification of the model, and illustrate the use of the magnetic susceptibility to follow the population dynamics of topological defects in this system, and its potential role in investigating a pattern melting phase transition.PACS numbers: