Altered transforming growth factor (TGF)-b expression levels have been linked to a variety of human respiratory diseases, including bronchopulmonary dysplasia and pulmonary fibrosis. However, a causative role for aberrant TGF-b in neonatal lung diseases has not been defined in primates.Exogenous and transient TGF-b1 overexpression in fetal monkey lung was achieved by transabdominal ultrasound-guided fetal intrapulmonary injection of adenoviral vector expressing TGF-b1 at the second or third trimester of pregnancy. The lungs were then harvested near term, and fixed for histology and immunohistochemistry.Lung hypoplasia was observed where TGF-b1 was overexpressed during the second trimester. The most clearly marked phenotype consisted of severe pulmonary and pleural fibrosis, which was independent of the gestational time point when TGF-b1 was overexpressed. Increased cell proliferation, particularly in a-smooth muscle actin-positive myofibroblasts, was detected within the fibrotic foci. But epithelium to mesenchyme transdifferentiation was not detected. Massive collagen fibres were deposited on the inner and outer sides of the pleural membrane, with an intact elastin layer in the middle. This induced fibrotic pathology persisted even after adenoviralmediated TGF-b1 overexpression was no longer evident.Therefore, overexpression of TGF-b1 within developing fetal monkey lung results in severe and progressive fibrosis in lung parenchyma and pleural membrane, in addition to pulmonary hypoplasia.
We report comparative studies of mini (6.3 Apelt e 2Lm p mm diameter electrodes) and medium sized (19 mm I diameter electrodes) pseudospark and back-lighted 355nm 6.3 m To Vacuum sysem thyratron (BLT) switches. Currents greater than 9 Laser kA, and hold-off voltages in excess of 40 kV have been achieved, the highest hold-off occurring in the smaller HV diameter switch. The switches are optically triggered; Load Resistor we consider here with helium and hydrogen fill. The results suggest that the switches can be optimized for miniaturized high voltage pulse generation, and that Fig.lExperimentalsetup smaller switches have potential for compact repetitiveThe inside structure of the mini-BLT and the mediumpulsed power applications.BLT is similar. For the mini-BLT, a 3mm thick molybdenum disk with a 3mm central hole is capped on a hollow OFHC 1/4" diameter copper tube. In the medium-BLT, a 15mm molybdenum disk with a 3mm central hole is I. INTRODUCTION inserted in a 3/4" diameter OFHC copper tube. 2mm electrodes gap is maintained in both the mini-BLT and the The pseudospark is a low pressure glow discharge medium-BLT. A 2.2Q stack resistor, 6nF or 1 5nF switch [1] which is distinguished from a traditional capacitor is included in the system. In order to reduce the thyratron by a self-heated, initially cold cathode that is system inductance, compact structure is installed. highly emissive (10,000A/cm2). The emission process involves initially a hollow cathode discharge mode, and a III. DIscusSION subsequent so-called super-emissive mode.The cathode does not require an external cathode heater. A. Hold-off Voltage Psuedospark lifetimes in excess of 108 shots have been The BLT is worked at the left side of the Paschen curve reported [2]. The optically triggered version of the switch in a low pressure glow discharge mode. Lower pressure is referred to as a Back-Lighted Thyratron (BLT), reflecting can result in higher hold-off voltage for the 2mm similarity between psuedosparks and thyratrons as low electrode distance. However, the higher gas pressure can pressure, high hold off voltages characteristics. bring smaller delay and jitter [3], reduce current quenching [4], and acquire higher maximum peak current. In addition, the gas discharge demands a certain critical II. EXPERIMENTAL SETUP gas density [5] which can be easily achieved in higher pressure. So, a comparative high pressure gas switch Fig. 1 shows the experimental system setup of the mini-without sacrificing high hold-off voltage is attractive.BLT (6.3mm electrode diameter) and the medium-BLT Fig. 2 shows that the mini-BLTs hold higher voltages (19mm electrode diameter). The mini-BLT is comprised than the medium-BLT under the same gas conditions. In of a glass cylinder 7.62cm (3 inch) long and 1.27cm (1/2 addition, helium can withstand higher breakdown voltage inch) in diameter. This is more than ten times smaller than than hydrogen such that an arc happens much more often the traditional thyratron and pseudospark in magnitude. in the medium-BLT than in the min...
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