Amplitude Modulation in Traveling Wave Tube Phase Modulator

Several problems of the amplitude modulation caused by the traveling wave tube used as a microwave phase modulator are discussed. Using Pierce's linear theory, some expressions for phase modulation and the amplitude modulation which occurs simultaneously are derived. From the derived composite modulation formula, various effects of the amplitude modulation on amplitude of carrier and each side band are calculated. To decrease amplitude modulation, experimental studies are performed by using the 1st anode to compensate it and a satisfactory improvement has been obtained

Crucial role of vinexin for keratinocyte migration in vitro and epidermal wound healing in vivo.

In the process of tissue injury and repair, epithelial cells rapidly migrate and form epithelial sheets. Vinexin is a cytoplasmic molecule of the integrin-containing cell adhesion complex localized at focal contacts in vitro. Here, we investigated the roles of vinexin in keratinocyte migration in vitro and wound healing in vivo. Vinexin knockdown using siRNA delayed migration of both HaCaT human keratinocytes and A431 epidermoid carcinoma cells in scratch assay but did not affect cell proliferation. Induction of cell migration by scratching the confluent monolayer culture of these cells activated both EGFR and ERK, and their inhibitors AG1478 and U0126 substantially suppressed scratch-induced keratinocyte migration. Vinexin knockdown in these cells inhibited the scratch-induced activation of EGFR, but not that of ERK, suggesting that vinexin promotes cell migration via activation of EGFR. We further generated vinexin (-/-) mice and isolated their keratinocytes. They similarly showed slow migration in scratch assay. Furthermore, vinexin (-/-) mice exhibited a delay in cutaneous wound healing in both the back skin and tail without affecting the proliferation of keratinocytes. Together, these results strongly suggest a crucial role of vinexin in keratinocyte migration in vitro and cutaneous wound healing in vivo

Stability of the compressible quantum Hall state around the half-filled Landau level

We study the compressible states in the quantum Hall system using a mean field theory on the von Neumann lattice. In the lowest Landau level, a kinetic energy is generated dynamically from Coulomb interaction. The compressibility of the state is calculated as a function of the filling factor $\nu$ and the width $d$ of the spacer between the charge carrier layer and dopants. The compressibility becomes negative below a critical value of $d$ and the state becomes unstable at $\nu=1/2$. Within a finite range around $\nu=1/2$, the stable compressible state exists above the critical value of $d$.Comment: 4 pages, 4 Postscript figures, RevTe

Theory of Current-Induced Breakdown of the Quantum Hall Effect

By studying the quantum Hall effect of stationary states with high values of injected current using a von Neumann lattice representation, we found that broadening of extended state bands due to a Hall electric field occurs and causes the breakdown of the quantum Hall effect. The Hall conductance agrees with a topological invariant that is quantized exactly below a critical field and is not quantized above a critical field. The critical field is proportional to $B^{3/2}$ and is enhanced substantially if the extended states occupy a small fraction of the system.Comment: 5 pages, RevTeX, final version to appear in PR