Circadian plasticity in honey bees

Circadian rhythms of about a day are ubiquitous in animals and considered functionally significant. Honey bees show remarkable circadian plasticity that is related to the complex social organization of their societies. Forager bees show robust circadian rhythms that support time-compensated sun-compass navigation, dance communication and timing visits to flowers. Nest-dwelling nurse bees care for the young brood around the clock. Here, we review our current understanding of the molecular and neuroanatomical mechanisms underlying this remarkable natural plasticity in circadian rhythms.

A Compact Dual-Band Circularly Polarized Antenna with Wide HPBWs for CNSS Applications

A compact dual-band circularly polarized antenna with wide half-power beamwidths (HPBWs) for compass navigation satellite system applications is proposed in this paper. The CP radiation is realized by arranging four compact dual-band inverted-F monopoles symmetrically to the center point, where the four monopoles are excited with a 90° phase offset through a compact sequential-phase feeding network. The compactness of the dual-band inverted-F monopole is realized by inserting two chip inductors in the horizontal portion of the monopole. The overall dimension of the antenna is only 0.211λ0 × 0.211λ0 × 0.057λ0, where λ0 is the corresponding free-space wavelength at 1.268 GHz. Experimental results show that the proposed antenna exhibits two overlapped impedance and axial ratio bandwidths of 50 MHz (1.236–1.286 GHz) and 40 MHz (1.532–1.572 GHz). Wide HPBWs of about 120°/125° and 121°/116° (XOZ/YOZ planes) at center frequencies (1.268, 1.561 GHz) of the CNSS-2 B3 and B1 bands are obtained, respectively. With these good performances, the antenna can be a good candidate for CNSS applications.

1. Early navigational cultures

Distinct geographies, where areas of sea were demarcated not only by land, but also by climate and current, helped to create different cultures of navigation that for centuries followed individual trajectories. ‘Early navigational cultures’ explains that the sky was one thing that was shared by ancient navigational cultures. It describes the techniques used by seamen in the Mediterranean, Pacific Ocean, Indian Ocean, and North Atlantic to register direction and position—the two fundamental variables of navigation. Before the use of a magnetic compass, navigation was also possible using other techniques such as coastal navigation (or pilotage), and a good understanding of tides, currents, swells, and behaviour of seabirds.