in this paper, the effects of scintillation phenomena on bit error rate (ber) and signal to noise ratio (snr), which are essential characteristics in free space optical (fso) communication system, are studied. until now various methods have been introduced to decrease ber and increase the link's reliability. optimizing snr is one of the fundamental methods to decrease ber value. intensity fluct...

We study a control system which includes several impulse modulators employing some kind of frequency modulation. It is shown how to chose periodic external actions in order to ensure the existence of a synchronous periodic mode, i.e. of such a mode that all the modulators emit impulses with the same frequency. 1 Problem Setting We consider an asynchronous impulsive system with m impulse modulat...

Mode competition of a free-electron laser is modeled by the Ginzburg-Landau equation. The stability of a single-mode solution is analyzed, and connections are established with known instabilities of the GinzburgLandau equation. It is found that the principal mode with the largest gain is always stable and hence there is no Benjamin-Feir instability. However, the Eckhaus ~or phase! instability g...

Let U and V be two independent normal random variables, and consider two new random variables X and Y of the form X = aU + bV, Y = cU + dV, where a, b, c, d, are some scalars. Each one of the random variables X and Y is normal, since it is a linear function of independent normal random variables.† Furthermore, because X and Y are linear functions of the same two independent normal random variab...

In Drosophila, the neuropeptide pigment-dispersing factor (PDF) is required to maintain behavioral rhythms under constant conditions. To understand how PDF exerts its influence, we performed time-series immunostainings for the PERIOD protein in normal and pdf mutant flies over 9 d of constant conditions. Without pdf, pacemaker neurons that normally express PDF maintained two markers of rhythms:...

The neuropeptide PDF promotes the normal sequencing of circadian behavioral rhythms in Drosophila, but its signaling mechanisms are not well understood. We report daily rhythmicity in responsiveness to PDF in critical pacemakers called small LNvs. There is a daily change in potency, as great as 10-fold higher, around dawn. The rhythm persists in constant darkness and does not require endogenous...