Similarity hypotheses for the atmospheric surface layer expressed by non-dimensional characteristic invariants - a review

In this paper, similarity hypotheses for the atmospheric surface layer (ASL) are reviewed using nondimensional characteristic invariants, referred to as π -numbers. The basic idea of this dimensional π-invariants analysis (sometimes also called Buckingham’s π-theorem) is described in a mathematically generalized formalism. To illustrate the task of this powerful method and how it can be applied to deduce a variety of reasonable solutions by the formalized procedure of non-dimensionalization, various instances are represented that are relevant to the turbulence transfer across the ASL and prevailing structure of ASL turbulence. Within the framework of our review we consider both (a) Monin-Obukhov scaling for forced-convective conditions, and (b) Prandtl-Obukhov-Priestley scaling for free-convective conditions.It is shown that in the various instances of Monin-Obukhov scaling generally two π-numbers occur that result in corresponding similarity functions. In contrast to that, Prandtl-Obukhov-Priestley scaling will lead to only one π number in each case usually considered as a non-dimensional universal constant. Since an explicit mathematical relationship for the similarity functions cannot be obtained from a dimensional π-invariants analysis, elementary laws of π-invariants have to be pointed out using empirical or/and theoretical findings. To evaluate empirical similarity functions usually considered within the framework flux-profile relationships, so-called integral similarity functions for momentum and sensible heat are presented and assessed on the basis of the friction velocity and the vertical component of the eddy flux densities of sensible and latent heat directly measured during the GREIV I 1974 field campaign

A multi-level cost benefit approach for regulatory decision support in food safety and quality assurance scenarios

In complex policy decision situations where policy objectives can only be reached through appropriate activities of individual actors with own decision authority and individual objectives, the classical approaches for measuring the effects of regulatory initiatives through cost-benefit or related types of analysis do not provide the appropriate information for decision support. This paper discusses a framework for a multi-level analysis approach that could provide decision support in multi-level policy decision situations.cost-benefit analysis, multi-level analysis, policy decision support, impact assessment, Food Consumption/Nutrition/Food Safety,

Editorial: Food System Dynamics

The food system involves all actors, activities, resources, and environments that produce and provide food to people wherever they are. It serves basic human needs and is as such of core relevance for human survival. It is global in production, consumption, and environmental impacts. But it is also deeply rooted in the social, cultural, natural, political, and legal environments of society. It needs to serve a diversity of consumer needs and lifestyles and has to cope with an organizational complexity where, a.o. small scale farms or enterprises interact with globally active industry or retail groups and where rural sites of production are remote from the urban and ever growing centers of consumption.Editorial, Food Consumption/Nutrition/Food Safety,

The Challenge of Reaching Transparency: ‘T-readiness’ of Enterprises and Sector Networks

Discussions on the safety and quality of food as well as growing interest in the sustainability of the production, distribution and consumption of food have contributed to the emergence of ‘transparency’ as a critical success factor for the food sector. However, reaching transparency for different stakeholders from different backgrounds and cultural identities is a dynamic process which depends on certain capabilities of enterprises and organizations along the food value chain but also on the realization of a fitting communication scheme within the sector. This discussion asks for the identification and utilization of an indicator that could identify deficiencies and support enterprises and the sector in reaching a level of transparency that could serve specified transparency needsAgribusiness, Agricultural and Food Policy, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Risk and Uncertainty,

Developments and Development Directions of Electronic Trade Platforms in US and European Agri-Food Markets: Impact on Sector Organization

Electronic trade platforms support trading transactions between enterprises. They have entered the business landscape including the agri-food sector only a few years ago. However, there already have been dramatic changes in the agri-food sectorÂ’s platform infrastructures. This paper analyzes developments in electronic trade platform infrastructures in the agri-food sector of the US and Europe between 2000 and 2002 and identifies development strategies of successful platforms. Of 85 platforms in existence in the year 2000, only 25 remained active in 2002. But there are still market entries of new platforms and existing platforms form various types of partnerships. The analysis could identify a range of strategic development lines of successful platforms. Initiating cooperation with other platforms on the use of specific features and the development and use of standards, gaining support by major market participants, the improvement of trading functionalities and the expansion of value-added services are the primary lines of development and evolvement of platforms. Platform evolvement tendencies and the present occurrence of the trade platform infrastructure allow for projecting the emergence of an agri-food sector with embedded, interconnected e-commerce infrastructure or mega-hub leading towards a more networked agri-food industry.Electronic commerce, Electronic trade platforms, Agri-food markets, Agribusiness, Marketing,