A New Feedback Method for Dy-namic Control of Manipulators

Asymptotic tracking and disturbance rejection in uncertain nonlinear systems is studied in the context of output feedback control. This study is facilitated by formalizing the notion ofk-fold exosystem and generalizing the internal model principle to the nonlinear setting

Evolutionary ecology of pipefish brooding structures:embryo survival and growth do not improve with a pouch

For animals that reproduce in water, many adaptations in life-history traits such as egg size, parental care, and behaviors that relate to embryo oxygenation are still poorly understood. In pipefishes, seahorses and seadragons, males care for the embryos either in some sort of brood pouch, or attached ventrally to the skin on their belly or tail. Typically, egg size is larger in the brood pouch group and it has been suggested that oxygen supplied via the pouch buffers the developing embryos against hypoxia and as such is an adaptation that has facilitated the evolution of larger eggs. Here, using four pipefish species, we tested whether the presence or absence of brood pouch relates to how male behavior, embryo size, and survival are affected by hypoxia, with normoxia as control. Two of our studied species Entelurus aequoreus and Nerophis ophidion (both having small eggs) have simple ventral attachment of eggs onto the male trunk, and the other two, Syngnathus typhle (large eggs) and S. rostellatus (small eggs), have fully enclosed brood pouches on the tail. Under hypoxia, all species showed lower embryo survival, while species with brood pouches suffered greater embryo mortality compared to pouchless species, irrespective of oxygen treatment. Behaviorally, species without pouches spent more time closer to the surface, possibly to improve oxygenation. Overall, we found no significant benefits of brood pouches in terms of embryo survival and size under hypoxia. Instead, our results suggest negative effects of large egg size, despite the protection of brood pouches

Passivity-Based Control

Stabilization of physical systems by shaping their energy function is a well-established technique whose roots date back to the work of Lagrange and Legendre. Potential energy shaping for fully actuated mechanical systems was first introduced in Takegaki and Arimoto (Trans ASME J Dyn Syst Meas Control 12:119--125, 1981) more than 30 years ago. In Ortega and Spong (Automatica 25(6):877--888, 1989) it was proved that passivity was the key property underlying the stabilization mechanism of these designs, and the, now widely popular, term of passivity-based control was coined. In this chapter we summarize the basic principles and some of the main developments of this controller design technique

Automatic Planning and Control of Robot Natural Motion Via Feedback

A feedback control strategy for the command of robot motion includes some limited automatic planning capabilities. These may be seen as sequential solution algorithms implemented by the robot arm interpreted as a mechanical analog computer. This perspective lends additional insight into the manner in which such control techniques may fail, and motivates a fresh look at requisite sensory capabilities. For more information: Kod*La

Large- and small-size advantages in sneaking behaviour in the dusky frillgoby Bathygobius fuscus

Sneaking tactic, a male alternative reproductive tactic involving sperm competition, is generally adopted by small individuals because of its inconspicuousness. However, large size has an advantage when competition occurs between sneakers for fertilization of eggs. Here, we suggest that both large- and small-size advantages of sneaker males are present within the same species. Large sneaker males of the dusky frillgoby Bathygobius fuscus showed a high success rate in intruding into spawning nests because of their advantage in competition among sneaker males in keeping a suitable position to sneak, whereas small sneakers had few chances to sneak. However, small sneaker males were able to stay in the nests longer than large sneaker males when they succeeded in sneak intrusion. This suggests the possibility of an increase in their paternity. The findings of these sizespecific behavioural advantages may be important in considering the evolution of size-related reproductive traits

Sperm displacement behavior of the cuttlefish Sepia esculenta (Cephalopoda: Sepiidae)

Sperm displacement behavior of cuttlefish (Sepia esculenta) was observed in a tank. Before ejaculation, male cuttlefish used their arms III to scrape out sperm masses attached to the buccal membranes of females. The removed sperm mass debris was directly visible and countable. Active sperm were present within the removed sperm debris, implying that the aim of this behavior is to remove competing male sperm. However, many sperm masses remained on the female buccal membrane even after the removal behavior, showing that sperm removal in S. esculenta is incomplete. The duration of sperm removal (an indicator of male investment in that process) was unaffected by the body sizes of mated pair, the duration of spermatangia placement at the current mating (for the hypothesis that the sperm removal serves to creat attachment space of spermatophores), or the estimated amount of sperm masses deposited from previous matings. Moreover, male S. esculenta performed sperm removal regardless of whether the last male to mate with the partner was himself, suggesting males remove not only the sperm of rivals but also their own. Although the number of removed sperm masses increased with the time spent on removal of sperm, male cuttlefish may shorten the duration of sperm removal to avoid the risk of mating interruption. We conclude that this time restriction would likely influence the degree of partial sperm removal in S. esculenta. A digital video image relating to the article is available at http://www.momo-p.com/showdetail-e.php?movieid=momo040729se01a