Information gain versus state disturbance for a single qubit

The trade-off between the information gain and the state disturbance is derived for quantum operations on a single qubit prepared in a uniformly distributed pure state. The derivation is valid for a class of measures quantifying the state disturbance and the information gain which satisfy certain invariance conditions. This class includes in particular the Shannon entropy versus the operation fidelity. The central role in the derivation is played by efficient quantum operations, which leave the system in a pure output state for any measurement outcome. It is pointed out that the optimality of efficient quantum operations among those inducing a given operator-valued measure is related to Davies' characterization of convex invariant functions on hermitian operators.Comment: 17 pages, LaTeX, osid.sty. Substantially expanded and generalize

A model of trophic flows in the northern Benguela upwelling system during the 1980s

A model of trophic flows through the northern Benguela between 1980 and 1989 was constructed using the ECOPATH approach. The model serves to close the temporal gap between models of the system for the 1970sand 1990s. The aim is to provide a workable model, with the intention of encouraging scientists working on different components of the ecosystem to collaborate to improve and update the model for more recent years.Ultimately, this type of model may form a basis for multispecies management approaches in the region. By the 1980s, sardine Sardinops sagax and hake Merluccius spp. stocks in the northern Benguela had both undergone a decline, yet were still heavily fished. Horse mackerel Trachurus trachurus capensis had increased over the previousdecade and was the dominant pelagic species during the 1980s, with high catches. Production by some groups, such as goby Sufflogobius bibarbatus, mesopelagic fish and demersal fish, was insufficient to sustainother components of the system. In all, 1.5 million tons of goby, 1.7 million tons of mesopelagic fish and 0.7 million tons of demersal fish (excluding hake) were required to support predators in the northern Benguela. Total biomass in the northern Benguela during the 1980s was high, comparable to that of the Peruvian system in the 1960s and almost double that of the northern Benguela during the 1970s. Horse mackerel and hake catches were both high, with fishing on hake being ecologically more expensive. Biomass of benthic producers, meioand macrobenthos were a quarter of the total biomass of these groups in the southern Benguela. The sensitivity of the model to parameter estimates is highlighted. Uncertainty about some of the parameters, thought to havemajor influences on the functioning of the model, is explored

MAXIMS: a computer program for estimating the food consumption of fishes from diel stomach contents data and population parameters

MAXIMS (Computer file), Food consumption, Stomach content, Population characteristics, Computer programmes Pisces

Comparing trophic flows in the southern Benguela to those in other upwelling ecosystems

A balanced trophic flow model of the southern Benguela ecosystem is presented, averaging the period 1980–1989 and emphasizing upper trophic levels. The model is based largely on studies conducted withinthe framework of the Benguela Ecology Programme and updates the results of an expert workshop held in Cape Town in September 1989. Small pelagic fish other than anchovy Engraulis capensis and sardineSardinops sagax, mainly round herring Etrumeus whiteheadi and mesopelagic fish, were important components of the food web in the southern Benguela. Severe balancing difficulties were encountered with respect to the semi-pelagic resources (hake Merluccius spp.) and demersal top predators (sharks), indicating the need for further research on the interaction of these groups with their ecosystem. The model is compared to other existing trophic flow models of ecosystems in major upwelling areas, i.e. the northern Humboldt Current (4–14°S), the California Current (28–42°N) and the southern Canary Current (12–25°N), and to twoindependently constructed models of the northern Benguela ecosystem. These models are compared using network analysis routines of the ECOPATH software, focusing on the interactions between the five dominantfish species (anchovy, sardine, horse mackerel Trachurus trachurus capensis, chub mackerel Scomber japonicus and hake) that support important fisheries in all systems. The upwelling systems rank by sizerather than species dominance. The ratio of catches and primary production differs between systems, partly because of differences in fishing regimes. Predation on the five dominant fish groups by other fish in the system was the most important cause of fish mortality in all models. Fishery catches are generally a larger cause of mortality for these groups than predation by mammals. The ecological cost of fishing appears to be comparatively low in the southern Benguela, because catches are low compared with the primary production, but also because the fishery is relatively low in the foodweb. However, in view of the very tight foodweb demonstrated in the model, it is likely that an increase in fishing pressure would cause severe trade-offs with respect to other components of the southern Benguela ecosystem

Estimating the food consumption of fishes: one step in linking a species with its ecosystem

Fish, Food consumption, Computer programs

On fitting Somer's equation for seasonally oscillating growth, with emphasis on T-subzero

Growth, Mathematical models

Exploring the use of neural networks for biomass forecasts in the Peruvian upwelling ecosystem

A pilot study was conducted to study the ability of an artificial neural network to predict the biomass of Peruvian anchoveta Engraulis ringens, given time series of earlier biomasses, and of environmental parameters (ocenographic data and predator abundances). Acceptable predictions of three months or more appear feasible after thorough scrutiny of the input data set

A sequential quadratic penalty method for nonlinear semidefinite programming

2003-2004 > Academic research: refereed > Publication in refereed journa