Computing the limits of risk aversion

Utility theory can be used to model the decision process involved in evaluating the cost-effectiveness of systems that protect against a risk to assets. A key variable in the model is the coefficient of relative risk aversion (or simply “risk-aversion”) which reflects the decision maker's reluctance to invest in such safety systems. This reluctance to invest is the scaled difference in expected utility before and after installing the safety system and has a minimum at some given value of risk-aversion known as the “permission point”, and it has been argued that decisions to sanction safety systems would be made at this point. As the cost of implementing a safety system increases, this difference in utility will diminish. At some point, the “point of indiscriminate decision”, the decision maker will not be able to discern any benefit from installing the safety system. This point is used to calculate the maximum reasonable cost of a proposed safety system. The value of the utility difference at which the decision maker is unable to discern any difference is called the “discrimination limit”.By considering the full range of accident probabilities, costs of the safety system and potential loss of assets, an average risk-aversion can be calculated from the model. This paper presents the numerical and computational techniques employed in performing these calculations. Two independent approaches to the calculations have been taken, the first of which is the derivative-based secant method, an extension of the referred derivative method employed in previous papers. The second is the Golden Bisection Method, based on a Golden Section Search algorithm, which was found to be more robust but less efficient than the secant method. The average risk-aversion is a function of several key parameters: the organisation's assets, the probability and maximum cost of an incident, and the discrimination limit. An analysis of the sensitivity of the results to changes in these parameters is presented. An average risk-aversion of 0.8–1.0 is found for a wide range of parameters appropriate to individuals or small companies, while an average risk-aversion of 0.1 is found for large corporations. This reproduces the view that large corporations will be risk neutral until faced with risks that pose a threat to their viability.     

Roteiros de Charme 旅馆协会 (巴西 )： 将好客与环境意识结合在一起

RoteirosdeCharme旅馆协会是一个包含了30个独立的宾馆、路边旅店和生态庇护所的非赢利性实体，它们采用了一种志愿的行为环境准则.除了它们对环境保护的承诺以外，许多RoteirosdeCharme成员也参与到专门涉及保存动物谱系、植物谱系或文化遗产的计划中去.有关该协会和行为准则的英文、西班牙文和葡萄牙文信息可以在www.roteirosdecharme.com.br中得到.     

Organ targeted prenatal gene therapy—how far are we?

Prenatal gene therapy aims to deliver genes to cells and tissues early in prenatal life, allowing correction of a genetic defect, before long-term tissue damage has occurred. In contrast to postnatal gene therapy, prenatal application can target genes to a large population of dividing stem cells, and the smaller fetal size allows a higher vector-to-target cell ratio to be achieved. Early-gestation delivery may allow the development of immune tolerance to the transgenic protein which would facilitate postnatal repeat vector administration if needed. Targeting particular organs will depend on manipulating the vector to achieve selective tropism and on choosing the most appropriate gestational age and injection method for fetal delivery. Intra-amniotic injection reaches the skin, and other organs that are bathed in the fluid however since gene transfer to the lung and gut is usually poor more direct injection methods will be needed. Delivery to the liver and blood can be achieved by systemic delivery via the umbilical vein or peritoneal cavity. Gene transfer to the central nervous system in the fetus is difficult but newer vectors are available that transduce neuronal tissue even after systemic delivery. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparisons of forager distributions from matched honey bee colonies in suburban environments

We conducted experiments designed to examine the distribution of foraging honey bees (Apis mellifera) in suburban environments with rich floras and to compare spatial patterns of foraging sites used by colonies located in the same environment. The patterns we observed in resource visitation suggest a reduced role of the recruitment system as part of the overall colony foraging strategy in habitats with abundant, small patches of flowers. We simultaneously sampled recruitment dances of bees inside observation hives in two colonies over 4 days in Miami, Florida (1989) and from two other colonies over five days in Riverside, California (1991). Information encoded in the dance was used to determine the distance and direction that bees flew from the hive for pollen and nectar and to construct foraging maps for each colony. The foraging maps showed that bees from the two colonies in each location usually foraged at different sites, but occasionally they visited the same patches of flowers. Each colony shifted foraging effort among sites on different days. In both locations, the mean flight distances differed between colonies and among days within colonies. The flight distances observed in our study are generally shorter than those reported in a similar study conducted in a temperate deciduous forest where resources were less dense and floral patches were smaller.     

Waste management in the leaf-cutting ant Acromyrmex echinatior: the role of worker size, age and plasticity

Division of labour is the hallmark of the success of many social animals. It may be especially important with regard to waste management because waste often contains pathogens or hazardous toxins and worker specialisation can reduce the number of group members exposed to it. Here we examine waste management in a fungus-farming, leaf-cutting ant, Acromyrmex echinatior, in which waste management is necessary to protect their vulnerable fungal crop. By marking ants with task-specific paint colours, we found clear division of labour between workers that engage in waste management and those that forage, at least during the fine timescale of the 3-day marking period. This division of labour was influenced by both age and size, with waste management workers tending to be smaller and younger than foragers. The role of preventing contaminated ants from entering the colony was fulfilled mainly by medium-sized workers. When the level of waste was experimentally increased, most of the ants that responded to remove the waste were workers previously engaged in tasks inside the nest rather than external waste workers or foragers. These responding workers tended to be young and medium-sized. Surprisingly, the responding ants were subsequently able to revert back to working within the fungus garden, but the probability of them doing so depended on their age and the length of time they were exposed to waste. The results demonstrate the importance of division of labour with regard to waste management in A. echinatior and show that this is adaptable to changing needs.     

Roteiros de Charme 旅馆协会 (巴西 )： 将好客与环境意识结合在一起

Roteiros de Charme 旅馆协会是一个包含了 30个独立的宾馆、路边旅店和生态庇护所的非赢利性实体，它们采用了一种志愿的行为环境准则 .除了它们对环境保护的承诺以外，许多 Roteiros de Charme成员也参与到专门涉及保存动物谱系、植物谱系或文化遗产的计划中去 .有关该协会和行为准则的英文、西班牙文和葡萄牙文信息可以在 www.roteirosdecharme.com.br中得到 .     

Diet quality and muscle tissue location influence consumer-diet discrimination in captive-reared rock lobsters (Panulirus cygnus)

Fundamental to the accuracy of stable isotope analysis in trophodynamic studies is the ability to predict discrimination between a consumer and its diet. Despite the widespread use of stable isotope analysis in trophic ecology, uncertainty still surrounds the factors affecting consumer-diet discrimination. Here we present evidence that diet quality and location of muscle tissue analysed affects the consumer-diet discrimination for the western rock lobster, Panulirus cygnus. Consumer-diet δ¹⁵N and δ¹³C discrimination for western rock lobster tail tissue were 1.67–2.97 and 2.92–3.60‰, respectively, with δ¹³C discrimination differing to values reported in the literature. Differences in nitrogen and carbon discrimination were observed between tail and leg tissue of lobsters of 1.22 and 1.13‰, respectively. Diet quality was also found to affect consumer-diet discrimination, with high protein pilchard diet leading to lower δ¹⁵N and higher δ¹³C discrimination. Diet quality should be considered as a factor that has the potential to affect consumer-diet discrimination when interpreting results from stable isotope studies.