Two-channel optical bistability and multistability in a degenerate four-level atomic medium under a static magnetic field.

In this paper, we study the formation of optical bistability (OB) and optical multistability (OM) in a degenerate four-level atomic system by an external magnetic field that is excited by a probe laser field, a coupling laser field and a signal laser field. The coupling field can cause electromagnetically induced transparency (EIT) for the probe field in the atomic medium, while the signal field and/or external magnetic field can switch between single-EIT and two-EIT regimes. Based on these properties, OB and OM effects can be formed at two different frequency regions of the probe field (two channels). By adjusting the magnetic field or the intensity and the frequency of laser fields, the threshold intensity and the width of OB or OM can also be changed simply. The model can be useful for experimental observations and applications in modern photonic devices.

Mechanism of physiological effects of titanium leaf sprays on plants grown on soil.

Titanium (Ti) has significant biological effects on plants, being beneficial at low and toxic at higher concentrations. From results of our hydroponical experiment with oats, we have recently proposed that the effect called hormesis is the mechanism of Ti action in plants. Here, we present the experiment with oats (Avena sativa L. cv. Zlat'ák) grown on soil where Ti was applied using leaf sprays. Two different soils, three different concentrations of Ti(IV) citrate spray solution (0, 20, and 50 mg Ti/kg), and three different Mg concentrations in each soil were tested. Some physiological parameters (dry and raw weights, top heights, chlorophyll content) and element contents (Mg, Fe, Zn, Mn) were determined. Ti showed considerable effects on all physiological parameters and the element's contents were determined. Differences between the two different soil types used was only in the strength of the effect of Ti; the trends remained unchanged. Generally, the effect of Ti is considerably weaker if Ti is applied on leaves than if being added to the nutrient solution. Thus, we confirm here that the action of Ti on plants could be explained by the hormesis effect.