Defects pinning centers

Several models have been proposed that consider the various interactions of the domain wall with electrostatically ordered defect pinning centers. These can be conditionally dassified into three different scenarios with respect to the charged defects destinations adopted during ordering ... 

Furthermore, EEL spectra of small Ag (n < 13) and Cu (n < 7) clusters show clear evidence for a size effect in their electronic structure [214]. The clusters were generated by sputtering with an UHV-compatible Xe-ion gun [45]. After size-selection with a quadrupole mass spectrometer, they have been deposited in situ in submonolayer quantities on a magnesium oxide film. Figure 1.44 displays EEL spectra taken at T = 45K for 0.04 ML of Ag (n < 13) clusters, deposited at low kinetic energy (Ek = 3-6eV) to prevent their fragmentation [215]. Each deposition was made on a freshly prepared film to avoid creation of defects, which are known to act as pinning centers for deposited clusters [216,217]. 

Significantly low defectiveness as compared to one-layer photomasks (pore-free films are obtained) since as a rule, the centers of lower Si layer crystallization do not coincide with the centers of upper Ni-P alloy layer crystallization transparent defects, pin holes and holes in the upper layer of Ni-P alloy are not continuation of transparent defects, pin holes and holes in the lower layer of Si. 

One of the methods of rising critical currents in conventional superconductors is the introduction of defects of structure which work as the pinning centers for the vortex lattice. This method can also be applied for doped fullerite. 

Table 7 provides the valu of iog /iog term for several types of defect clusters (MNDO force field model) [93]. It is shown that for the defects of types A and B (Fig. 7) these values are rather large, and endohedral clusters significantly influence the properties of the superconductive state. However, utilization of endohedral clusters as the pinning centers requires further research because in the fiame of this approach it is not possible to take into account electron-phonon interactions. 

In contrast to conventional superconductors, thermal fluctuations of the vortex positions become very important in high-Tc materials, in particular close to Hc2(T). This is a consequence of both the small coherence length and the fact that the pinning centers in the cuprates are mainly provided by point defects. 

Stacking faults. If extra CuO layers are inserted adjacent to the chain plane of YBCO, this tends to a local structure of the defects resembling that of the so-called Y124 phase. These may act as important pinning centers for H cy but are not important for H c- From a practical point of view these are not suitable pinning centers as it is no possible to prepare samples with or without stacking faults. 

Oxygen defects. Daumling et al. observed a peak in the magnetization hysteresis in oxygen-deficient single crystals at an intermediate field, which they ascribed to flux pinning. This kind of pinning center is not the most important one. 

Defects in crystals are known to have a potentially major influence on phase behavior. For instance, dislocation unbinding is believed to be central to the 2D melting transition, while in 3D there is evidence to suggest that defects can act as nucleation centers for the liquid phase [105]. In superconductors, defects can pin vortices and influence vortex melting [106]. 

The deeper understanding of the dynamics of feedback-induced drift allows us to propose robust and efficient methods to move a spiral center from a given initial location along an arbitrary path to a desired final position. In this way, we can avoid eventually existing defects in the medium that could pin the spiral wave. This result might be important for such possible application as low-voltage defibrillation of cardiac tissue. 

Translations-Translations Consider the centering pin mechanism in Fig. 2, consisting of a base, a block, and a pin. The upper plane of the base is represented with a magnified bow defect, to which local coordinate frame OpE is associated. The goal is to model the effects of this small geometrical defect on the FR (the pin s axis), to which coordinate frame OpR is also associated. 

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