Ecology and power in the periphery of Maasina : the case of the Hayre in the nineteenth century

This article explores political tensions between successive nineteenth-century rulers of the inland delta of the Niger in central Mali (the Fulbe Diina of Hamdullahi and the Futanke successors of al-Hajj Umar) and the pastoral interests of the Fulbe chiefdoms on their eastern periphery, in a region known as the Hayre. A close study of changing forms of local governance and natural resource management demonstrates that although different strategies were employed by the Fulbe and Futanke states to control the Hayre, the internal dynamics of the region can only partly be explained by the influence of these central powers

Uniform asymptotics of the coefficients of unitary moment polynomials

Keating and Snaith showed that the $2k^{th}$ absolute moment of the characteristic polynomial of a random unitary matrix evaluated on the unit circle is given by a polynomial of degree $k^2$. In this article, uniform asymptotics for the coefficients of that polynomial are derived, and a maximal coefficient is located. Some of the asymptotics are given in explicit form. Numerical data to support these calculations are presented. Some apparent connections between random matrix theory and the Riemann zeta function are discussed.Comment: 31 pages, 1 figure, 2 tables. A few minor misprints fixe

Entropy of complex relevant components of Boolean networks

Boolean network models of strongly connected modules are capable of capturing the high regulatory complexity of many biological gene regulatory circuits. We study numerically the previously introduced basin entropy, a parameter for the dynamical uncertainty or information storage capacity of a network as well as the average transient time in random relevant components as a function of their connectivity. We also demonstrate that basin entropy can be estimated from time-series data and is therefore also applicable to non-deterministic networks models.Comment: 8 pages, 6 figure

Bond percolation on isoradial graphs: criticality and universality

In an investigation of percolation on isoradial graphs, we prove the criticality of canonical bond percolation on isoradial embeddings of planar graphs, thus extending celebrated earlier results for homogeneous and inhomogeneous square, triangular, and other lattices. This is achieved via the star-triangle transformation, by transporting the box-crossing property across the family of isoradial graphs. As a consequence, we obtain the universality of these models at the critical point, in the sense that the one-arm and 2j-alternating-arm critical exponents (and therefore also the connectivity and volume exponents) are constant across the family of such percolation processes. The isoradial graphs in question are those that satisfy certain weak conditions on their embedding and on their track system. This class of graphs includes, for example, isoradial embeddings of periodic graphs, and graphs derived from rhombic Penrose tilings.Comment: In v2: extended title, and small changes in the tex

Control of human gait stability through foot placement

During human walking, the centre of mass (CoM) is outside the base of support for most of the time, which poses a challenge to stabilizing the gait pattern. Nevertheless, most of us are able to walk without substantial problems. In this review, we aim to provide an integrative overview of how humans cope with an underactuated gait pattern. A central idea that emerges from the literature is that foot placement is crucial in maintaining a stable gait pattern. In this review, we explore this idea; we first describe mechanical models and concepts that have been used to predict how foot placement can be used to control gait stability. These concepts, such as for instance the extrapolated CoM concept, the foot placement estimator concept and the capture point concept, provide explicit predictions on where to place the foot relative to the body at each step, such that gait is stabilized. Next, we describe empirical findings on foot placement during human gait in unperturbed and perturbed conditions. We conclude that humans show behaviour that is largely in accordance with the aforementioned concepts, with foot placement being actively coordinated to body CoM kinematics during the preceding step. In this section, we also address the requirements for such control in terms of the sensory information and the motor strategies that can implement such control, as well as the parts of the central nervous system that may be involved. We show that visual, vestibular and proprioceptive information contribute to estimation of the state of the CoM. Foot placement is adjusted to variations in CoM state mainly by modulation of hip abductor muscle activity during the swing phase of gait, and this process appears to be under spinal and supraspinal, including cortical, control. We conclude with a description of how control of foot placement can be impaired in humans, using ageing as a primary example and with some reference to pathology, and we address alternative strategies available to stabilize gait, which include modulation of ankle moments in the stance leg and changes in body angular momentum, such as rapid trunk tilts. Finally, for future research, we believe that especially the integration of consideration of environmental constraints on foot placement with balance control deserves attention

Session E8: Efficiency Measurements as Tool in Evaluating Fishways

Abstract: The awareness of the importance of free fish migration in the Netherlands is reflected in the increasing number of fishways that has been built in the past decade. The intention is that all the bottlenecks will be solved before 2027. Equally important as the realization of fishways, is the evaluation of the design. In other words, are all species and size classes that want to pass, truly able to pass the structure. The challenge in this type of research is to avoid interference of the measuring tools with the fish migrants. The conventional monitoring fyke, does not meet this requirement. Migration is obstructed and the gear is highly selective for small fish. Emerging electronic techniques offer this opportunity and makes it possible to watch fish migration behaviour on the road through the fishway. The use of a resistivity Fish Counter will be illustrated by means of a case study. The counter detects the swimming direction and size of the passing fish. Species identification is achieved by the application of a camera, triggered by the passing fish. The placement of a counter station at both sides of the fishway, gives the unique opportunity to determine the efficiency in terms of the ratio between the number of fish entering the downstream side and the number of fish exiting at the upstream side. An example will be given of a fishway that originally was reviewed as a good functioning construction. However, measurements of the efficiency showed that only a small part of the fish community was able to pass. The results also uncovered the weak spot in the design. This was not regarded as a failure, but as an opportunity to make use of the hidden potential of this fishway. It also contributed to the improvement of this type of design in general

Q-Dependent Susceptibilities in Ferromagnetic Quasiperiodic Z-Invariant Ising Models

We study the q-dependent susceptibility chi(q) of a series of quasiperiodic Ising models on the square lattice. Several different kinds of aperiodic sequences of couplings are studied, including the Fibonacci and silver-mean sequences. Some identities and theorems are generalized and simpler derivations are presented. We find that the q-dependent susceptibilities are periodic, with the commensurate peaks of chi(q) located at the same positions as for the regular Ising models. Hence, incommensurate everywhere-dense peaks can only occur in cases with mixed ferromagnetic-antiferromagnetic interactions or if the underlying lattice is aperiodic. For mixed-interaction models the positions of the peaks depend strongly on the aperiodic sequence chosen.Comment: LaTeX2e, 26 pages, 9 figures (27 eps files). v2: Misprints correcte