Keldysh Green's function approach to coherence in a non-equilibrium steady state: connecting Bose-Einstein condensation and lasing

Solid state quantum condensates often differ from previous examples of condensates (such as Helium, ultra-cold atomic gases, and superconductors) in that the quasiparticles condensing have relatively short lifetimes, and so as for lasers, external pumping is required to maintain a steady state. On the other hand, compared to lasers, the quasiparticles are generally more strongly interacting, and therefore better able to thermalise. This leads to questions of how to describe such non-equilibrium condensates, and their relation to equilibrium condensates and lasers. This chapter discusses in detail how the non-equilibrium Green's function approach can be applied to the description of such a non-equilibrium condensate, in particular, a system of microcavity polaritons, driven out of equilibrium by coupling to multiple baths. By considering the steady states, and fluctuations about them, it is possible to provide a description that relates both to equilibrium condensation and to lasing, while at the same time, making clear the differences from simple lasers

DIEP flap for breast reconstruction: Is abdominal fat thickness associated with post-operative complications?

Some surgeons consider a high body mass index (BMI) or important abdominal fat excess as contraindications for breast reconstruction with free deep inferior epigastric perforator (DIEP) flap. This study aimed to identify factors associated with post-operative complications by using this type of flap, with an emphasis on BMI and abdominal subcutaneous fat thickness. A retrospective chart review of 105 consecutive patients who underwent DIEP flap breast reconstruction at our institution was performed to assess post-operative complications. Among other risk factors, we specifically studied the influence of BMI and abdominal wall thickness on complication occurrence. Abdominal wall thickness was measured at 10 different points on the angio-computed tomography scan performed pre-operatively. Median age was 49.8 years (range, 27-69); average BMI was 25.57 kg/m(2) (range, 18.07-41.91). Immediate breast reconstruction was performed for 35% of patients, and five patients (4.7%) underwent bilateral reconstruction. Twenty-six patients (24.8%) presented 29 post-operative complications; 12 concerned abdominal complications (delayed wound healing [n = 6] and seroma [n = 6]) and 17 were related to complications of the reconstructed breast (six minimal necrosis treated conservatively, eight minor necrosis requiring surgical debridement and three total flap loss). The complication rate was not correlated with increased BMI or abdominal wall thickness. The only factor that significantly predicts DIEP flap complications was pre-operative radiotherapy (odds ratio = 4.05; p = 0.03). No significant correlation was observed between BMI of 25-35 kg/m(2) or abdominal wall thickness and post-operative complications of the donor site or DIEP flap. Therefore, these factors should not be considered as contraindication criteria