A Bethe theory for the directional dependence of stopping by molecules

We derive a Bethe formula for the stopping of swift ions by target molecules oriented with respect to the beam. The theory is characterized by a directional mean excitation energy formed from transition energies and dipole matrix elements. The expression for the mean excitation energy is similar to the one for an isotropic sample but the dipole matrix elements corresponding to the various transition moment directions carry unequal weights which depend on the orientation of the molecule with respect to the beam. For a large class of molecules, the logarithm of the mean excitation energy is linear in sin² θ, where θ denotes the angle between the beam and the principal molecular axis. We illustrate the properties of the theory in the simple case of a diatomic molecule.     

Interface structure and strength of ultrasonically wedge bonded heavy aluminium wires in Si-based power modules

In this paper the microscopical structure of wedge bonded interfaces is investigated, with a focus on what effect the power in the ultrasonic bonding and the initial microscopical structure of the \(Al\) wire have on the quality of the bonding. The quality evaluation is based on mapping the microscopical restructuring of the wire grains during bonding and thereby assessing the effective bonding area. Three approaches are utilized in the interface characterization: mechanical shear test, optical microscopy combined with micro-sectioning, and scanning electron microscopy assisted by focused ion beam milling. The shear test is applied to quantify the strength of the bonded interfaces, while the other methods are used to map the grain reconstruction caused by the bonding. From the results it is possible to map a 3D image of the wire deformation, and the grain refinement region which is the dominating parameter with respect to fatigue related cracking of the interfaces. It is found that the bonding power, as well as the initial wire structure directly affects the refinement region and thereby the strength of the interface.     

Affordances revisited: Articulating a Merleau-Pontian view

This article takes a renewed look at the concept of “affordance.” It points out that the concept is being used within the CSCL community in ways which signify an underlying disagreement concerning the exact ontological nature and epistemological status of an “affordance.” Such disagreement, it is argued, is a problem for both design and empirical research. Because HCI discussions of the concept have informed CSCL, views presented within this discourse are discussed. A Merleau-Pontian account of affordances is developed, building on his view of the human being as always already being-in-the world in a non-thematized, pre-reflective correspondence of body and world in the concrete activity. A dynamic, agent-centred, cultural-, experience- and skill-relative, but perception-independent, ontology is proposed for affordances. Toward the end of the article, examples are given of how the Merleau-Pontian account of affordances may shift the focus of empirical research and of design processes within CSCL.     

Hierarchical multi-level computer network for laboratory automation

The design and implementation of a microcomputer network to support laboratory automation is described and discussed. It is a multi-level hierarchical star network connected to a multiprogrammed computer on which all program development is done. The system is capable of supporting a large number of experimental setups. The microcomputers are either used as (1) local microcomputers for experiment control, (2) multiplexers for other microcomputers or (3) controllers for peripherals known in the multiprogrammed computer. The system combines the advantages of a large multiprogrammed computer with those of a small cheap dedicated computer close to the experiment. Character-oriented peripherals are connected to the multiprogrammed computer only. This reduces the amount of system software to be written for the network by an order of magnitude and eliminates the need for interfacing to existing small computer software. The system software consist of three small programs (monitors) providing a process concept and multibuffering of data in the involved computers. The monitor establishes a hierarchy of control and they eliminate the need for any local load device for the microcomputers as their monitors are in a read-only store. The system developed is designed for control of experiments in an environment where the experiments and the control strategies change with time and where the data refinement required is beyond what can be done on the present generation of microcomputers.     

Web 2.0: Inherent tensions and evident challenges for education

In upper tertiary educational programmes around the world, the new Web-mediated communication practices termed Web 2.0 are introduced as learning activities with the goal of facilitating learning through collaborative knowledge construction. The aim of this paper is to point to discrepancies in the views of learning, knowledge, and the goals of the practice implicit in Web 2.0 and educational practices and to argue that these discrepancies lead to theoretical tensions and practical challenges when Web 2.0 practices are utilized for educational purposes. The article is structured into four main parts: First, Web 2.0 is characterized from a practice perspective. Second, some conceptual discrepancies between the “practice logics” of Web 2.0 and educational practices are identified. Third, the question of transcending the discrepancies is raised through a discussion of related pedagogical strategies. Fourth, it is argued that the conceptual discrepancies bear out in practice as concrete challenges concerning collaboration, evaluation, and the general aim and status of the material produced by students. These challenges are illustrated with examples from the author’s practical experience with Web 2.0-mediated learning activities in eight courses at the BA and MA levels.