Phototaxic foraging of the archaepaddler, a hypothetical deep-sea species

An autonomous agent (animat, hypothetical animal), called the (archae) paddler, is simulated in sufficient detail to regard its simulated aquatic locomotion (paddling) as physically possible. The paddler is supposed to be a model of an animal that might exist, although it is perfectly possible to view it as a model of a robot that might be built. The agent is assumed to navigate in a simulated deep-sea environment, where it hunts autoluminescent prey. It uses a biologically inspired phototaxic foraging-strategy, while paddling in a layer just above the bottom. The advantage of this living space is that the navigation problem is essentially two-dimensional. Moreover, the deep-sea environment is physically simple (and hence easier to simulate): no significant currents, constant temperature, completely dark. A foraging performance metric is developed that circumvents the necessity to solve the travelling salesman problem. A parametric simulation study then quantifies the influence of habitat factors, such as the density of prey, and the body-geometry (e.g. placement, direction and directional selectivity of the eyes) on foraging success. Adequate performance proves to require a specific body-% geometry adapted to the habitat characteristics. In general performance degrades smoothly for modest changes of the geometric and habitat parameters, indicating that we work in a stable region of 'design space'. The parameters have to strike a compromise between on the one hand the ability to 'fixate' an attractive target, and on the other hand to 'see' as many targets at the same time as possible. One important conclusion is that simple reflex-based navigation can be surprisingly efficient. In the second place, performance in a global task (foraging) depends strongly on local parameters like visual direction-tuning, position of the eyes and paddles, etc. Behaviour and habitat 'mould' the body, and the body-geometry strongly influences performance. The resulting platform enables further testing of foraging strategies, or vision and locomotion theories stemming either from biology or from robotics

Do Macroeconomic Announcements Cause Asymetric Volatility?

In this paper we study the impact of macroeconomic news announcementson the conditional volatility of stock and bond returns. Using dailyreturns on the S&P 500 index, the NASDAQ index, and the 1 and 10 yearU.S. Treasury bonds, for January 1982 - August 2001, some interestingresults emerge. Announcement shocks appear to have a strong impact onthe (dynamics of) bond and stock market volatility. Our resultsprovide empirical evidence thatasymmetric volatility in the Treasurybond market can be largely explained by these macroeconomicannouncement shocks. This suggests that the asymmetric volatilityfound in government bond markets are likely due to misspecification ofthe volatility model. After including macroeconomic announcements intothe model, the asymmetry disappears. Becausefirm-specific news is themost important source of information in the stock market, theasymmetries in stock volatility do not disappear after incorporatingmacroeconomic announcements into the volatility model.Asymmetry;Announcement Effects;Multivariate GARCH;Stock and Bond Market;Time-Varying Covariances

Energy production and use in Dutch agriculture

Energy relationschips in the agriculture of one of the most densely populated areas of the world, the Nether lands, are described. The Netherlands appear selfsupporting in food energy. However, if one takes account of energy consumption in horticulture, the direct and indirect fossil energy cost exceeds the food energy produced in agriculture. An input-output analysis to estimate the indirect energy is applied on Japanese data. It appears that in Japanese agriculture for every unit energy used directly, two units are used indirectly. Energy relationships are different for the main agricultural sectors. In the primary production sector more energy is produced than consumed (9 : 1), while in the secondary production sector and in the horticulture the oppositie holds (1 : 7). The energy input of the secondary production sector, however, is mainly of plant origin. Energy balances of an arable farm at present and around 1800 are given to show in more detail in which way food energy is and was produced. Possible ways to diminish the fossil energy input of the modern farm are discussed

The utility of a digital simulation language for ecological modeling

Dynamic modeling of ecological phenomena has been greatly facilitated by the recent development of continuous system simulator programs. This paper illustrates the application of one of these programs, S/360 Continuous System Modeling Program (S/360 CSMP), to four systems of graduated complexity. The first is a two species system, with one feeding on the other, using differential equations with constant coefficients. The second and third systems involve two competing plant species in which the coefficients of the differential equations are varying with time. The final example considers the management of a postulated buffalo herd in which the dynamics of the herd population and composition by sex and age is combined with various strategies to control its size and to optimize buffalo production

Computing with quantized enveloping algebras: PBW-type bases, highest-weight modules, R-matrices

Let Uqg be the quantized enveloping algebra corresponding to the semisimple Lie algebra g We describe algorithms to obtain the multiplication table of a PBWtype basis of Uqg We use this to obtain an algorithm for calculating a Grobner basis of an ideal in the subalgebra U which leads to a general construction of irreducible highestweight modules over Uqg We also indicate how to compute the corresponding Rmatrice

Constructing canonical bases of quantized enveloping algebras

An algorithm for computing the elements of a given weight of the canonical basis of Uqg is described