John E. Harris

The Role of Endogenous Rhythms in Vertical Migration

Photographic recording at hourly intervals of a group of animals contained in a small tank kept in continuous darkness has revealed a 24 h cycle of locomotor activity in Daphnia magna and in Calanus helgolandic A change in periodicity of the rhythm in Daphnia kept under continuous illumination suggests that the cycle is not determined by external stimuli The phasing of the cycle differs in the two animals, but in both there is an increase in activity during the hours of darkness. In Calanus and possibly also in Daphnia, the cycle of activity is absent in the winter months.

A note on the breeding season, sex ratio and embryonic development of the dogfish Scyliorhinus canicula (L.)

Records of nearly 2000 dogfish collected from the Ilfracombe region suggest that the spawning season of this fish starts in November and continues at least until July. This area probably represents a spawning ground into which the females migrate during the spawning season; the males follow them much later in April and May. Figures are given to show the time taken at different temperatures for the embryo to develop to a series of definite morphological stages; these suggest that the temperature characteristic of the development (µ = 20,000) is substantially the same as for several teleost species.

Phase discrimination in chromatic compound gratings

Phase discrimination thresholds were measured for yellow/green isoluminant and non-isoluminant compound gratings in which the amplitude of the two components (f and 3f) was twice the detection threshold. The phase discrimination threshold at isoluminance was worse than in all the other conditions, which gave broadly similar threshold data. It is suggested that this is due to a positional uncertainty in the neural representation of the isoluminant stimuli.

Magnification factor for adaptation of a visual transient mechanism

After adaptation by an observer to a patch of gradually increasing (or decreasing) luminance, a steady test patch appeared to be gradually dimming (or brightening). These aftereffects did not transfer interocularly. Adaptation to a checkerboard, in which the white squares gradually dimmed while the black squares gradually brightened, gave an aftereffect that was a pattern of intersecting diagonal lines, that is, an extremely blurred checkerboard. The larger the squares of the checkerboard were, the farther into the periphery the aftereffect extended, because small squares were blurred out by the summation areas of the underlying visual channels, which were larger at increasing eccentricities and had diameters of 20 times the resolvable dot separation. The estimated visual acuity of these channels was as low as 20/400. These estimates were confirmed by manipulating separately the local and space-averaged luminances of the adapting stimulus.

Spectrum sharing for M2M applications through Whitetime exploitation in WiFi networks

The demand placed on wireless networks operating within fixed allocations of licensed or unlicensed spectrum has introduced the development of cognitive radios, capable of intelligently utilising spare resource whenever it is available. Since WiFi is an ubiquitous method for localized high speed mobile internet access it exists in almost all typical radio environments however the spectrum in which it operates is not exploited to its full potential. This paper introduces a concept called Whitetime to describe the free time between frame transmissions on a typical WiFi channel and across all networks. Initial measurements of real environments indicate that more than 85% of time on a channel is unused however this predominantly consists of short interframe spaces. Detailed analysis reveals periods of inactivity greater than 10ms are synchronised with the beacon interval from observable access points on the channel. For applications that require opportunistic network access such as non deterministic machine to machine (M2M) communication, Whitetime presents a reliable opportunity to transmit packets as long as 1500 bytes using standard physical layer techniques.

The Potential of Offloading and Spectrum Sharing for 5G Vehicular Infotainment

This paper explores the possibility of opportunistic cognitive radio based offloading for infotainment services in future autonomous vehicles. With the goal of a truly intelligent vehicle, research into the potential of vehicular communications intends to facilitate a wide range of services from safety aspects such as collision prevention to in-car information and entertainment (infotainment) services. With such a broad remit, future vehicles will likely have to rely on multiple communication technologies to successfully service their needs. In this paper we identify the benefits of offloading to WiFi via Drive-thru Internet in vehicular applications but note the damaging handover overheads introduced by such schemes. Instead we propose a method of opportunistic access based on Beacon Interval Whitetime to macro-cellular WiFi access points as a means of sustaining an active connection whilst moving through an urban environment. This will reduce the inefficiencies of successive handovers and enable increased volumes of content to be delivered to the vehicle. We perform an empirical study of the potential for offloading in a representative urban environment and find periods of upto 100 ms per second are available for opportunistic use throughout the test. Additionally we find semi-deterministic opportunities for cognitive access occur following 35% of beacons observed on a WiFi channel.