Thermal Activation of the Crystallization Kinetics of Amorphous Silicon

Solid Phase Crystallization of amorphous silicon films, deposited by the Low Pressure Chemical Vapor Deposition technique, is studied by in-situ monitoring the film conductance. The crystal growth rate VG, deduced from this measurement, was found to be thermally activated. The activation energy E behaviour for films with different doping varying in a great range, from undoped to 4×1019 cm−3, was then deduced. This behaviour, described for the first time in this work, shows a constant E for undoped and weak doping, then a high decrease after a doping value threshold. The undoped films show a decreasing E when the deposition rate increases i.e. when the structure of the amorphous deposited film tends to correspond to the relaxed amorphous network. All these new results are used to introduce a crystallization model based on a crystalline-amorphous double phase and on the charge of defects at the crystal-amorphous interface.

Current practice in Marfan's syndrome and annulo-aortic ectasia: aortic root replacement with a composite graft over a twenty-year period

BACKGROUND

From October 1973 to December 1995, 251 patients (204 male, 47 female) aged from 10 to 75 years (mean: 46.6 +/- 15) underwent an ascending aortic replacement with a composite graft for: dystrophic aneurysm (AN), 168 cases (66.9%); chronic dissection (CD), 36 cases (14%); and type A acute dissection (AD), 48 cases (19.1%). Fifty-one patients (20.3%) suffered from Marfan's disease (25 AN, 17 AD, 9 CD). Thirty-seven patients (14.7%) had undergone a previous cardiac or aortic operation. The ascending aortic replacement was extended to the transverse arch in 31 patients (12.3%). A mechanical valve was used in 233 patients (92.8%). The classic "Bentall" technique was used in 87 patients (34.6%), the "button" technique in 121 patients (48.2%), the "Cabrol" technique in 26 patients (10.3%) and a "mixed" technique in 17 patients (6.2%).

RESULTS

The hospital mortality accounts for 7.2% (18 out of 251) (AN: 4 out of 68, 2.3%, CD: 4 out of 36, 11.1%, AD: 9 out of 48, 18.7%). When emergencies are considered, the hospital mortality is 12 out of 54 (22.2%) versus 6 out of 197 (3%) in elective procedures. The predictors of hospital death were emergency, AD (p < 0.03) and arch replacement (p < 0.02). Mean follow up is 38 +/- 15 months (4-262). The overall long term survival rate is (Kaplan Meïer): 92 +/- 6% at one year, 77.9% +/- 9% at 5 years, 67.7 +/- 12% at 10 years, and 61.3 +/- 15% at 12 years. The 10-year survival rate is significantly higher in patients with AN (93 +/- 6%) than in patients with AD (61.6 +/- 17%) (p < 0.01). The late survival rate is also significantly higher after the "button" (93.8 +/- 5%) or Bentall's reimplantation (88.7 +/- 6%, 83.8 +/- 9%, and 76.6 +/- 12%) than after the "Cabrol" procedure (80 +/- 18%, 63 +/- 21% and 58 +/- 35%) at 1, 5, and 8 years, respectively.

CONCLUSION

Ascending aortic replacement with a composite graft is a safe procedure, especially when performed electively in patients with dystrophic aneurysm or Marfan's disease. The technique of coronary reimplantation has a significant influence of the long-term results, with the reimplantation of choice being the "button" technique. The "Cabrol" technique must be used when the "button" or the "Bentall" reimplantation is not feasible.

Tumor necrosis factor-alpha induces changes in the phosphorylation, cellular localization, and oligomerization of human hsp27, a stress protein that confers cellular resistance to this cytokine

The stress protein hsp27 is constitutively expressed in several human cells and shows a rapid phosphorylation following treatment with tumor necrosis factor-alpha (TNF-alpha). hsp27 usually displays native molecular mass ranging from 100 to 700 kDa. Here, we have analyzed the TNF-alpha-mediated changes in the phosphorylation, cellular localization, and structural organization of hsp27 in HeLa cells. We report that the TNF-alpha-mediated hsp27 phosphorylation is a long-lasting phenomenon that correlates with the cytostatic effect of this cytokine. Following TNF-alpha treatment, the rapid phosphorylation of hsp27 occurred concomitantly with complex changes in the intracellular distribution and structural organization of this protein. This resulted in the quantitative redistribution of hsp27 toward the soluble phase of the cytoplasm. In addition, during the first 2 h of TNF-alpha treatment, a transient increase in the native molecular mass of most hsp27 molecules (< or = 700 kDa) occurred. Then, by 4 h of TNF-alpha treatment, the native size of this stress protein drastically regressed (< 200 kDa). During this phenomenon, the phosphorylated isoforms of hsp27 remained concentrated in the small or medium-sized oligomers (< 300 kDa) of this protein. We also analyzed the properties of human hsp27 in transfected murine L929 cell lines that constitutively express this protein. In these cells, TNF-alpha induced modifications in the phosphorylation, intracellular distribution, and oligomerization of human hsp27 similar to those observed in HeLa cells. Moreover, the expression of hsp27 in L929 cells was found to correlate with a reduced cytotoxicity of this cytokine. Hence, the complex changes in the phosphorylation, intracellular locale and structural organization of human hsp27 may be related to the protective activity of this protein against the deleterious effects induced by TNF-alpha.