ABSTRACT
This study examines the performance of peak-clipped optical BPSK-SSB signal. The effectiveness of peak clipping for PAPR reduction and the degradation caused by peak clipping are numerically analyzed. PAPR of optical BPSK-SSB signal becomes high because of the peaky Hilbert-transformed signal component. PAPR improvement of 43.7% is attained by clipping the peaks of the Hilbert-transformed signal. Assessment of spectral degradation reveals that both waveform clipping and modulator nonlinearity contribute to sideband suppression degradation. Analyses of the 100-km transmitted signal results show that PAPR reduction by peak clipping alleviates the nonlinear phase shift caused by self-phase modulation (SPM), which produces a less degraded signal at the detector. Peak clipping can improve the SPM threshold of the studied system by 2.63 dB.
ABSTRACT
Osteogenic protein-1 (OP-1/BMP-7), a member of the transforming growth factor (TGF-beta) superfamily of proteins, is shown to be expressed at sites of epithelial-mesenchymal tissue interaction during human fetal development. In the present study, we examined the expression of OP-1 in human placentas (5-11 weeks of gestation and full term) using in situ hybridization and immunohistochemistry methods. The results show that OP-1 was expressed in cytotrophoblasts (Langhans layer) of the chorionic villi in early and full term placentas. Employing highly purified cytotrophoblast cultures which fused to form functional syncytiotrophoblasts, we showed that exogenously added recombinant OP-1, in the presence of low serum concentration, reduced the secretion of chorionic gonadotropin and progesterone by 60% and 36%, respectively, compared with control cultures. The results suggest that osteogenic protein-1 is synthesized locally by cytotrophoblasts and may be involved in the regulation of human pregnancy by controlling reproductive hormonal secretion.
