Skin flaps

Flaps can reconstruct defects of the integument, resurface mucosal defects, as well as contribute to contour. They are used where grafting is not feasible because of the nature of the defect and/or where the aims of reconstruction would be better served by vascularized tissue with both cutaneous and subcutaneous components. A skin flap can also be combined with fascia, muscle, or bone to reconstruct a complex or composite defect, and to provide tissue to restore function. Flaps may be classified according to the origin of the flap: local skin flaps are raised from tissue adjacent to the defect (usually deriving their blood supply from the subcutaneous tissue and subdermal plexus), and distant flaps are raised on dedicated vascular pedicles from a non-contiguous region. A distant flap may be moved to the defect maintaining the continuity of the pedicle (a ‘regional’ or ‘pedicled’ flap) or as a free flap, where the flap is elevated from its remote donor site and the pedicle is divided to allow the flap to be transported ‘free’ to the defect and then the vascular continuity is re-established by anastomosis to a recipient vessel in the defect. This chapter focuses on local flaps.

Quantitative Study on MFL Signal of Pipeline Composite Defect Based on Improved Magnetic Charge Model

Pipeline magnetic flux leakage (MFL) internal detection technology is the most widely used and effective method in the field of long-distance oil and gas pipeline online detection. With the improvement of data quantization precision, the influence of stress on MFL signal has been paid more and more attention. In this paper, the relationship between stress and saturation magnetization is introduced based on J-A theory. The analytical model of MFL detection signal for pipeline composite defects is established. The MFL signal characteristics of composite defects are quantitatively calculated. The effect of stress on MFL signal is studied. The theoretical analysis is verified by experimental data and excavation results. The researches show that the saturation magnetization of ferromagnets decreases exponentially with the increase of stress in strong magnetic field. The MFL signal of composite defect is weaker than that of volumetric defects of the same dimension. The axial amplitude and radial peak-to-peak value of MFL signal decrease with the increase of stress around the defect. The axial amplitude and radial peak-to-peak value of MFL signal increase non-linearly with the increase of width and depth of defects. When using MFL signal to judge the defect depth, it is necessary to make clear whether there is stress concentration phenomenon around the defect because the stress will lead to underestimation of the defect depth.