Alteration of membrane surface charges represents one of the most interesting effects of the electromagnetic exposure on biological structures. Some evidence exists in the case of extremely low frequency whereas the same effect in the radiofrequency range has not been detected. Changes in transmembrane voltages are probably responsible for the mobilization of intracellular calcium described in some previous studies but not confirmed in others. These controversial results may be due to the cell type under examination and/or to the permeability properties of the membranes. According to such a hypothesis, calcium oscillations would be a secondary effect due to the induced change in the membrane voltage and thus dependent on the characteristics of ionic channels present in a particular preparation. Calcium increases could suggest more than one mechanism to explain the biological effects of exposure due to the fact that all the cellular pathways using calcium ions as a second messenger could be, in theory, disturbed by the electromagnetic field exposure. In the present work, we investigate the early phase of the signal transmission in the peripheral nervous system. We present evidence that the firing rate of rat sensory neurons can be modified by 50/60 Hz magnetic field but not by low level 900 MHz fields. The action of the 50/60 Hz magnetic field is biphasic. At first, the number of action potentials increases in time. Following this early phase, the firing rate decreases more rapidly than in control conditions. The explanation can be found at the single-channel level. Dynamic action current recordings in dorsal root ganglion neurons acutely exposed to the electromagnetic field show increased functionality of calcium channels. In parallel, a calcium-activated potassium channel is able to increase its mean open time.

We show that localized (nonevanescent) solutions to Maxwell equations exist, which propagate without distortion along normal waveguides with superluminal speed.

Some experiments, performed at Berkeley, Cologne, Florence, Vienna, Orsay and Rennes led to the claim that something seems to travel with a group velocity larger than the speed c of light in vacuum. Various other experimental results seem to point in the same direction: For instance, localized wavelet-type solutions of Maxwell equations have been found, both theoretically and experimentally, that travel with Superluminal speed. Even muonic and electronic neutrinos — it has been proposed — might be "tachyons," since their square mass appears to be negative. With regard to the first-mentioned experiments, it was very recently claimed by Guenter Nimtz that those results with evanescent waves or "tunneling photons" — implying Superluminal signal and impulse transmission — violate Einstein causality. In this note, on the contrary, we want to stress that all such results do not place relativistic causality in jeopardy, even if they refer to actual tachyonic motions: In fact, special relativity can cope even with Superluminal objects and waves. For instance, it is possible (at least in microphysics) to solve also the known causal paradoxes, devised for "faster than light" motion, even if this is not widely recognized. Here we show, in detail and rigorously, how to solve the oldest causal paradox, originally proposed by Tolman, which is the kernel of many further tachyon paradoxes. The key to the solution is a careful application of tachyon mechanics, as it unambiguously follows from special relativity.

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We analyze the transition from passive mode locking into the novel modulational-instability regime of erbiumdoped fiber lasers. By including in the cavity an anisotropic loss, we observed, depending on the polarization setting, the generation of either single pulses as short as 435 fs or a continuous-wave train of 3.5-ps-long solitons at a repetition rate of 76 GHz. Even with no anisotropic losses in the cavity, soliton trains at a repetition rate of as high as 130 GHz were still observed. We believe that this is the first observation of a self-induced modulational-instability laser.