Domain boundary motion

Main processing effects on achieving materials with a high relative permeability is the minimization of the formation of particles (mainly carbides and sulfides) which may impede domain boundary motion, and induc-... 

Many other examples of extended dislocations exist. Their further discussion will be deferred to the section on planar defects except for the case of superlattice dislocations. The ordered Cuj Au structure and antiphase domains have already been described in the introduction. While (a/2)<110> is a lattice translation vector in the face-centered cubic structure, it is not a lattice translation vector in ordered CujAu. Motion of a dislocation with b = ( /2)<110> in the ordered CujAu creates an antiphase domain boundary. Motion of a second dislocation through the structure with the same b restores the perfect order since a<110> is a lattice translation vector the structure of CujAu is simple cubic. Pairs of imperfect dislocations with, for example, b = (fl/2)[110] are thus expected. Such pairs, called superlattice dis-... 

In figure A3.3.9 the early-time results of the interface fonnation are shown for = 0.48. The classical spinodal corresponds to 0.58. Interface motion can be simply monitored by defining the domain boundary as the location where i = 0. Surface tension smooths the domain boundaries as time increases. Large interconnected clusters begin to break apart into small circular droplets around t = 160. This is because the quadratic nonlinearity eventually outpaces the cubic one when off-criticality is large, as is the case here. 

Figure 12. Tunneling to the alternative state at energy e. can be accompanied by a distortion of the domain boundary and thus populating the ripplon states. The doubled circles denote atomic tunneling displacements. The dashed hne signifies, say, the lowest energy state of the wall, and the dashed circles correspond to the respective atomic displacements. An alternative wall s state is shown by dash-dotted lines the corresponding alternative sets of atomic motions are coded by dash-dotted lines. The domain boundary distortion is diown in an exagerated fashion. The boundary does not have to lie in between atoms and is drawn this way for the sake of argument its position in fact is not tied to the atomic locations in an a priori obvious fashion.

S.M. Allen and J.W. Cahn. Microscopic theory for antiphase boundary motion and its application to antiphase domain coarsening. Acta Metall., 27(6) 1085-1095, 1979. 

A metallic glass containing 80% Fe and 20% B is an excellent soft magnetic material because there are no grain boundaries to obstruct domain wall motion. 

With this approach we can uncover, in an unprecedented detail, how a single fluorescent dye molecule travels through linear or strongly curved sections of the hexagonal channel system, how it changes speed, and how it bounces off a domain boundary with a different channel orientation. Furthermore, we can show how molecular travel is stopped at a less ordered region, or how lateral motions between leaky channels allow a molecule to explore different parallel channels within an otherwise well-ordered periodic structure. 

Hence the velocity and pressure distributions at 0(1) can be completely determined within the core region (away from the end walls), to within an arbitrary constant for p 0). In fact, the flow is a simple unidirectional flow, as is appropriate for traction-driven flow between two plane surfaces. The turning flow that must occur near the ends of the cavity influences the core flow only in the sense that the presence of impermeable end walls requires a pressure gradient in the opposite direction to the boundary motion in order to satisfy the zero-mass-flux constraint. But now, a remarkable feature of the domain perturbation procedure is that we can use our knowledge of the unidirectional flow that is appropriate for an undeformed interface at 0(1) to directly determine the 0(5) contribution to the interface shape function in (6-159a) without having to determine any other feature of the solution at 0(5). 

In practice, of course, drifting motions will simply sweep the spiral tip to the domain boundary where the spiral will annihilate. Such boundary annihilations - a highly desirable effect in the context of defibrillation - can be understood as a cancellation with the anti-rotating mirror image spiral after local reflection through the Neumann boundary condition. Below, we do not pursue such modifications due to bounded domains. 

Although the superstructural morphology of Hytrel has been studied extensively, little molecular-level information is availaUe in the solid state. In particular, we would like to characterize the domain boundaries and the nature of the phase separation. We would like to understand molecular motion in this polymer, both in the rigid domains and in the moUle regions. Also, we would like to clarify the relationships between molecular motion, chemical composition, and mechanical properties. 

The diffusive permeability coefficient P was determined from the hydraulic permeability coefficient K measured in a temperature range of 273-333° K according to the method described by Yasuda and Peterlin. The In P - 1/T plot shows a distinct jum at about 304° K for membrans with 45 and 60 wt.% of EBBA. It corresponds to the crystalline-nematic phase transition of EBBA. This important increase of P values is probably due to the transition in EBBA which may induce the activation of molecular motion of PC or to the creation of larger vacancies fraction around the domain boundary of EBBA. In that way the water molecules may diffuse faster. Pure PC films do not exhibit that type of behaviour, and the temperature dependence of P does not show, in that temperature range, any significant changes. 

It should be noted that the LEED patterns observed for halogen adsorption on the bcc surfaces can also be explained by regularly spaced antiphase domain boundaries [82B]. Such models, however, yield unrealistically small distances between the adsotbed halogen atoms and require complicated concerted motion of the adatoms to obtain continuously varying LEED patterns [82J], Further, electronic band stmcture studies performed on chemisorbed halogen layers on Fe(llO) support the formation of the incommensurate compression phases described above [91M],... 

We can further characterize the structure by the distribution function of u in Fig.7. At low temperature the motion of each particle is nearly harmonic, so that the distribution function is Gaussian. As the temperature increases, the distribution becomes asymmetric, and above it is symmetric again and almost independent of temperature. At 850 K we have found a phase alternation between the aj and a phases, which correspond to the experimental observation that the domain boundary between the two phases is constantly vibrating just below Tc [37]. We cannot tell exactly whether Tc is below or above 850 K in this simulation because the system size is too small. At 900 K the MD-synthesized quartz is clearly in the / ... 

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