Articulating User Needs in Collaborative Design: Towards an Activity-Theoretical Approach

This paper analyses the collaborative design ofa high-technology product, a neuromagnetometerused in the analysis of the activity of thehuman cortex. The producer, Neuromag Company istrying to transform the device from a basicresearch instrument into a means of clinicalpractice. This transition is analyzed as asimultaneous evolution of the product,producer-user network and user activities. Thenetwork is analyzed as a network of activitysystems. Each activity has a historicallyformed object and a motive of its own, as wellas a system of cultural means and expertise. Weuse these to explain and understand theinterests and points of view of the actors inrelation to the product and the contradictionsof the producer-user network. It is suggestedthat the emerging user needs of collectiveactors must be analyzed at three levels. At thefirst level, the use value of the product, itscapacity of solving the vital problems andchallenges of developing user activities, ischaracterized. The second-level analysisconcerns the creation and development of thenecessary complementary tools and services thatmake the implementation and use of the productpossible. This task presupposes collaborationbetween several communities of the innovationnetwork. The third level is the situatedpractical use of the product. In ourexperience, it is advantageous that researcherscontribute with their data to a dialogue inwhich the user needs are articulated.     

Thermal Cycling Reliability of Sn-Ag-Cu Solder Interconnections. Part 1: Effects of Test Parameters

The work presented in part 1 of this study focuses on identifying the effects of thermal cycling test parameters on the lifetime of ball grid array (BGA) component boards. Detailed understanding about the effects of the thermal cycling parameters is essential because it provides means to develop more efficient and meaningful methods of reliability assessment for electronic products. The study was carried out with a single package type (BGA with 144 solder balls), printed wiring board (eight-layer build-up FR4 structure), and solder interconnection composition (Sn-3.1Ag-0.5Cu) to ensure that individual test results would be comparable with each other. The effects of (i) temperature difference (ΔT), (ii) lower dwell temperature and lower dwell time, (iii) mean temperature, (iv) dwell time, and (v) ramp rate were evaluated. Based on the characteristic lifetimes, the thermal cycling profiles were categorized into three lifetime groups: (i) highly accelerated conditions, (ii) moderately accelerated conditions, and (iii) mildly/nonaccelerated conditions. Thus, one might be tempted to use the highly accelerated conditions to produce lifetime statistics as quickly as possible. However, to do this one needs to know that the failure mechanisms do not change from one lifetime group to another and that the failure mechanisms correlate with real-use failures. Therefore, in part 2 the observed differences in component board lifetimes will be explained by studying the failure mechanisms that take place in the three lifetime groups.     

The Reliability of Microalloyed Sn-Ag-Cu Solder Interconnections Under Cyclic Thermal and Mechanical Shock Loading

In this study, the performance of three microalloyed Sn-Ag-Cu solder interconnection compositions (Sn-3.1Ag-0.52Cu, Sn-3.0Ag-0.52Cu-0.24Bi, and Sn-1.1Ag-0.52Cu-0.1Ni) was compared under mechanical shock loading (JESD22-B111 standard) and cyclic thermal loading (40 ± 125°C, 42 min cycle) conditions. In the drop tests, the component boards with the low-silver nickel-containing composition (Sn-Ag-Cu-Ni) showed the highest average number of drops-to-failure, while those with the bismuth-containing alloy (Sn-Ag-Cu-Bi) showed the lowest. Results of the thermal cycling tests showed that boards with Sn-Ag-Cu-Bi interconnections performed the best, while those with Sn-Ag-Cu-Ni performed the worst. Sn-Ag-Cu was placed in the middle in both tests. In this paper, we demonstrate that solder strength is an essential reliability factor and that higher strength can be beneficial for thermal cycling reliability but detrimental to drop reliability. We discuss these findings from the perspective of the microstructures and mechanical properties of the three solder interconnection compositions and, based on a comprehensive literature review, investigate how the differences in the solder compositions influence the mechanical properties of the interconnections and discuss how the differences are reflected in the failure mechanisms under both loading conditions.     

Protecting probiotic bacteria by microencapsulation: challenges for industrial applications

The use of probiotic bacteria in novel foods to provide beneficial health effects is today of increasing interest in the food industry. The process stability of probiotics is, however, not always optimal. Microencapsulation technology can be used to maintain the viability of probiotic bacteria during food product processing and storage. Both true microcapsules with coating as well as microspheres where the bacteria are evenly spread in the coating material are discussed. It is important that encapsulation keeps the probiotics active through the gastrointestinal tract and releases them in their target organ. The survival of microencapsulated cells in simulated gastric conditions is therefore also reviewed. Polysaccharides like alginate, gellan, κ-carrageenan and starch are the most commonly used materials in microencapsulation of bifidobacteria and lactobacilli. Techniques commonly applied for probiotic microencapsulation are emulsion, extrusion, spray drying, and adhesion to starch. Bead stability can be improved by using different coating materials, e.g. chitosan. Future challenges in the field include recognition of new potent applications, selection of appropriate techniques, materials and bacterial strains, and minimizing the extra costs incurred by microencapsulation.     

Joining silicon nitride to itself and to metals

This article reviews the progress that has been made in developing and applying joining techniques for Si₃N₄ and discusses our understanding of the influence of process selection on the materials science of the formation and properties of joints. High-performance Si₃N₄ joints can be produced, but it is clear that much work remains to be done before the use of such joints in hot-stressed applications can be disregarded as a problem.     

Heat generation in high power prismatic Li‐ion battery cell with LiMnNiCoO2 cathode material

While in use, battery modules and battery packs generate large amounts of heat, which needs to be accounted for. The main challenge in battery thermal management is the correct estimation of heat generation in the battery cell during charging/discharging. In this paper, a method to calculate accurate heat generation in one individual cell is provided. The heat generation is calculated by measuring the overpotential resistances with four different methods and entropic heat generation in the cell. The effect and contribution of entropic heat generation towards the total heat generation in the cell are also calculated and measured. Finally, calorimeter tests are carried out to compare the calculated and measured heat generation. The results indicate that except for direct current resistance measured by impedance spectroscopy, all the overpotential resistances are very close to each other. Copyright © 2014 John Wiley & Sons, Ltd.     

Hierarchically Designed Bioactive Glassy Nanocoatings for the Growth of Faster and Uniformly Dense Apatite

Crack‐free bioactive nanocoatings embedded with uniformly distributed silica‐rich bioactive spherical aggregates were successfully prepared in situ by controlling the micellization of a SiO₂–CaO–P₂O₅ sol using the tri‐block copolymer P123 followed by dip‐coating onto a bio‐inert glass substrate and calcined. These hierarchically designed nanocoatings embedded with such bioactive glassy nanospheres (BGNS) enabled to induce the deposition of a densely populated, uniform, and well‐developed needlelike crystalline carbonated hydroxyapatite coating reminiscence of the mineral phase of natural bone within a short immersion time in simulated body fluid. The BGNS nanocoatings also supported the growth and attachment of human gingival fibroblasts. The results suggest that these newly designed composite nanocoatings are noncytotoxic, capable of supporting rapid and homogeneous calcium phosphate deposition as well as subsequent crystallization, and likely to be promising candidates for inert glass reinforced bone implants.     

Functional and sensory properties of hen eggs with modified fatty acid compositions

Foaming, emulsifying, gelling, and sensory properties of fresh and stored hen eggs fed with a diet supplemented with flax oil (FO), rapeseed oil (RO), fish oil (FISH), and by-product from black currant processing (BC) were investigated. With these diets, the ω6/ω3 fatty acid ratio of eggs varied from 1.5 to 5.8, while the ratio for eggs in the control group was 6.2. Compared to eggs in the control group, FO supplementation in the feed had statistically significant influences on the foaming properties of the fresh eggs. Eggs stored for 21 days lost part of their foaming properties in FISH oil supplemented group, but the foaming properties in all test groups were technically acceptable. The emulsifying properties of eggs in FO and FISH supplemented feeding groups were statistically different compared to control group. In boiled eggs, flax oil and fish oil supplementation induced off flavours in eggs, but no changes between the control group and test groups were found in the sensory properties of mayonnaise preparations. These results suggest that the egg processing industry may produce egg-based products using oil-supplemented eggs without major problems in functional or sensory properties.