Conceptual design of pointing control systems for space station gimballed payloads

A conceptual design of the control system for Payload Pointing Systems (PPS) is developed using classic Proportional-Integral-Derivatives (PID) techniques. The major source of system pointing error is due to the disturbance-rich environment of the space station in the form of gimbal baseplate motions. These baseplate vibrations are characterized using Fast Fourier Transform (FFT) techniques. Both time domain and frequency domain dynamic models are developed to assess control system performance. Three basic methods exist for the improvement of PPS pointing performance: increase control system bandwidth, add Image Motion Compensation, and/or reduce (or change) the baseplate disturbance environment

Mating system and population genetic structure of the bulldog ant Myrmecia pavida

Understanding the evolution of the alternative mating strategies of monandry and polyandry is a fundamental problem in evolutionary biology because of the cost-benefit trade-offs associated with mating for females. The problem is particularly intriguing in the social insects because queens in most species appear to be obligately monandrous (i.e., only a single male fathers their offspring), while those in a minority of species have evolved high, and sometimes extreme, polyandry. One group which may shed particular insight is the ant subfamily Myrmeciinae (Myrmecia and Nothomyrmecia). Here we examine the population and colony genetic structure of the bulldog ant Myrmecia pavida CLARK, 1951 by genotyping offspring workers from 45 colonies. We find little evidence of geographic structuring or inbreeding in the population, indicating that the species outbreeds, most probably in mating swarms. We also find that queens of M pavida show moderately high polyandry, with 84% having mated with between two and seven males, and an overall mean observed mating frequency of 3.8. This is significantly higher than previously reported for queens of Nothomyrmecia macrops, in which most females mate singly. This was similar to that of M pyriformis, M brevinoda, and M pilosula, the three congenerics for which mating frequencies have recently been reported. The two genera in the Myrmeciinae therefore appear to show multiple transitions in mating frequency and further investigation of the subfamily may be highly informative for disentangling the forces driving the evolution of alternative mating strategies

Specific appetites in the domestic fowl

The development and expression of specific appetites for calcium, sodium and thiamine in the fowl were studied. It was found that calcium -deprived chickens exhibited a preference for diets supplemented with calcium carbonate or calcium lactate. There was no immediate preference, but a group preference characteristically built up over a period of days, suggesting that learning plays a role in the development of this appetite. It is specifically for calcium, in that strontium, the element most closely related to calcium, is not selected. Experiments investigating the importance of visual and gustatory cues showed that selection could still occur when only visual, or only taste cues were available, though selection tended to be less efficient under these circumstances. No appetite could be demonstrated in the complete absence of these cues. A mildly unpleasant flavour such as calcium lactate may act as a helpful cue, but a more aversive taste, such asquinine, blocks the preference for calcium. The importance of hedonic responses is emphasised by the failure of deficient birds to select solutions of calcium salts, though they show a preference for a suspension of calcium carbonate, which is rather more palatable. Calcium deprivation leads to an increase in appetitive pecking behaviour when chickens are presented with a range of different stimuli in an open arena, although deprived and normal birds show similar preferential responses. The effects of deprivation could not be simulated in normal birds by the administration of parathyroid hormone, and it was'concluded that this hormone does not exert a direct effect on the behaviour. An experiment to measure the effects of deprivation on birds in an activity cage yielded ambiguous results. The importance of need reduction in the development of calcium preference was assessed. Exclusive access to a supplemented diet for as long as four days was necessary before a preference was noted. However, injection of a very small quantity of a calcium salt had a profound effect in delaying the development of the preference. Expression of the appetite could not be inhibited by administering drugs - either a depressant, like alcohol, or a true tranquillising agent. Taken as a whole, these results suggest that ingestion of calcium may exert its reinforcing action by means of a general effect on 'well- being', rather than upon some particular site of action, such as the skeletal system, or by means of some specific mechanism, such as anxiety reduction. The fowl differs from the rat in that novelty plays no part in the development of a specific appetite. A less detailed study was carried out on the effects of sodium and of thiamine deficiency. Both normal and sodium- deprived chickens avoid saline solutions. Deprived birds were indifferent to food supplemented with sodium chloride, and there was no avidity for sodium when a functional deficiency was induced by a non -dietary method. The only behavioural effect observed in these sodium - deprived chickens was an increase in appetitive pecking activity, similar to that seen in the calcium -deprived birds. It was concluded that the fowl, unlike the domestic rat and other mammals, does not exhibit a specific appetite for sodium. On the other hand, a specific appetite for a thiamine -supplemented diet was readily demonstrable after a deficient state had been induced by feeding a metabolic antagonist. The significance of these results was discussed in an evolutionary context, and they were related to the nutritional requirements of the fowl in a natural habitat

Division of labour and risk taking in the dinosaur ant, Dinoponera quadriceps

The success of social insects can be largely attributed to division of labour. In contrast to most social insects, many species with simple societies contain workers which are capable of sexual reproduction. Headed by one or a few reproductive individuals, subordinate workers form a dominance hierarchy, queuing to attain the reproductive role. In these species task allocation may be influenced by individual choice based on future reproductive prospects. Individuals with a better chance of inheriting the colony may be less likely to take risks and high-ranking workers that spend a greater amount of time in proximity to the brood may be able to increase the ability to police egg-laying by cheating subordinates. We investigated division of labour and risk taking in relation to dominance rank in the queenless ponerine ant, Dinoponera quadriceps, a species with relatively simple societies. Using behavioural observations, we show that high-ranking workers spend more time performing egg care, less time foraging and are less likely to defend the nest against attack. High-rankers also spent a greater amount of time guarding and inspecting eggs, behaviours which are likely to improve detection of egg laying by cheating subordinates. We also show that high-ranking workers spend a greater amount of time idle, which may help increase lifespan by reducing energy expenditure. Our results suggest that both risk-taking and egg-care behaviours are related to future reproductive prospects in D. quadriceps. This highlights a mechanism by which effective division of labour could have been achieved during the early stages of eusocial evolution

Log-periodic modulation in one-dimensional random walks

We have studied the diffusion of a single particle on a one-dimensional lattice. It is shown that, for a self-similar distribution of hopping rates, the time dependence of the mean-square displacement follows an anomalous power law modulated by logarithmic periodic oscillations. The origin of this modulation is traced to the dependence on the length of the diffusion coefficient. Both the random walk exponent and the period of the modulation are analytically calculated and confirmed by Monte Carlo simulations.Comment: 6 pages, 7 figure

Sanitizing the fortress: protection of ant brood and nest material by worker antibiotics

Social groups are at particular risk for parasite infection, which is heightened in eusocial insects by the low genetic diversity of individuals within a colony. To combat this, adult ants have evolved a suite of defenses to protect each other, including the production of antimicrobial secretions. However, it is the brood in a colony that are most vulnerable to parasites because their individual defenses are limited, and the nest material in which ants live is also likely to be prone to colonization by potential parasites. Here, we investigate in two ant species whether adult workers use their antimicrobial secretions not only to protect each other but also to sanitize the vulnerable brood and nest material. We find that, in both leaf-cutting ants and weaver ants, the survival of the brood was reduced and the sporulation of parasitic fungi from them increased, when the workers nursing them lacked functional antimicrobial-producing glands. This was the case for both larvae that were experimentally treated with a fungal parasite (Metarhizium) and control larvae which developed infections of an opportunistic fungal parasite (Aspergillus). Similarly, fungi were more likely to grow on the nest material of both ant species if the glands of attending workers were blocked. The results show that the defense of brood and sanitization of nest material are important functions of the antimicrobial secretions of adult ants and that ubiquitous, opportunistic fungi may be a more important driver of the evolution of these defenses than rarer, specialist parasites