Managing requirements specifications for product lines - An approach and industry case study

Software product line development has emerged as a leading approach for software reuse. This paper describes an approach to manage natural-language requirements specifications in a software product line context. Variability in such product line specifications is modeled and managed using a feature model. The proposed approach has been introduced in the Swedish defense industry. We present a multiple-case study covering two different product lines with in total eight product instances. These were compared to experiences from previous projects in the organization employing clone-and-own reuse. We conclude that the proposed product line approach performs better than clone-and-own reuse of requirements specifications in this particular industrial context.     

Ride comfort optimization of a city bus

Ride comfort optimization of a city bus is considered in this article, using stiffness and related damping of the power unit mounts as design variables. The response of the bus, due to road irregularities, is calculated in the time domain by using a finite element (FE) model describing the complete vehicle. The body of the bus is condensed, using a substructuring technique, in order to reduce the simulation times. Operational deflection shapes (ODS) have been used to compare measured and calculated vibrations and some corrections of the FE model have been done. The response, i.e. acceleration, at three locations in the bus has been frequency-weighted according to the comfort standard ISO 2631:1997. The resulting root mean square (RMS) values of these responses are then used in the objective functions in the optimization procedure. The computational results show that it is possible to increase the ride comfort. However, the improvement of the ride comfort is probably too small to have a substantial subjective impact on the passenger in the bus. The results show that the objective function, regarding the overall ride comfort in the bus, has local optima. Received October 10, 1999     

Thermal diffusivity measurements of some synthetic CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> slags

In an attempt to systematize the knowledge of the heat conduction of liquid silicates, the effective thermal diffusivities of some synthetic slags containing CaO, Al₂O₃, and SiO₂ have been measured, using the three-layer laser-flash method on a differential scheme in the temperature range of 1625 to 1825 K. The effective thermal diffusivities measured, which are a combination of the phononic and photonic heat-transfer mechanisms, were found to increase with increasing temperature for all the presently investigated slags. The slag compositions were chosen in such a way that the changes in the effective thermal diffusivities would reflect the changes in the structure of the slags. It was observed that, at a CaO/Al₂O₃ molar ratio of 4.42, an increase of the SiO₂ content had very little effect on the effective thermal diffusivity values. On the other hand, addition of SiO₂ to a slag with the CaO/Al₂O₃ molar ratio of 2.59 resulted in a significant increase in the effective thermal diffusivity. The addition of Al₂O₃ to slags with a constant CaO/SiO₂ molar ratio resulted in a marked increase in the effective thermal diffusivity. Both these trends indicate that there might be an influence of the network formation in silicate melts on the effective thermal diffusivity.     

In-plane contributions to phase contrast in intermittent contact atomic force microscopy

Contrast in the phase response of intermittent-contact atomic force microscopy (IC-AFM) reveals in-plane structural and mechanical properties of polymer monolayers. This result is unexpected, as IC-AFM has previously only been considered as a probe of out-of-plane properties. Until now, AFM measurements of nanoscale in-plane properties have employed contact mode techniques. In-plane property measurements are possible with intermittent contact AFM because there is a small but significant component of tip motion parallel to the sample surface. This in-plane component of tip displacement is virtually universal in AFM, implying that oscillating-tip techniques generally are sensitive to in-plane material properties. We present a simple Hertzian model of intermittent-contact AFM that includes such an in-plane displacement.     

Effect of muscle,ageing time and modified atmosphere packaging conditions on the colour,oxidative and microbiological stability of packed beef

The objective of this study was to evaluate the influence of two different vacuum ageing times (7 and 14 days) and the impact of the modified atmosphere packaging (MAP) configuration (gas/product ratios: 0.5 and 1 and gas composition: 70% O₂ + 30% CO₂ and 40% O₂ + 30% CO₂ + 30% N₂) on the quality of fresh beef during subsequent storage at 4 °C. For this purpose, three separate experiments were performed. For each experiment, two different muscles (Longissimus dorsi and Biceps femoris) were sampled from four double‐muscled Belgian Blue beef carcasses. Next to colour, also the evolution in microbial load, pH, O₂ and CO₂ in the headspace and lipid oxidation at the meat surface were evaluated. A vacuum ageing for 14 days compared with 7 days resulted in a higher initial microbial load on the day of MAP packaging, which resulted finally in a significantly shorter shelf life. This ageing effect was less pronounced on the colour stability and lipid oxidation of the meat samples. No significant influence of the packaging configuration on any of the analysed parameters (colour, microbial load, pH and lipid oxidation at the meat surface) was observed.     

Effects on milk urea concentration,urine output,and drinking water intake from incremental doses of potassium bicarbonate fed to mid-lactation dairy cows

Large variation exists in the potassium content of dairy cow feeds and also within a feed type due to soil type and fertilization. Increased ration K concentration causes a subsequent increase in urinary volume and could be expected to also lower milk urea concentration. Six multiparous mid-lactation Swedish Red dairy cows, all fitted with rumen cannulas, were subjected to 3 different levels of K intake in a Latin square experiment with three 2-wk periods to evaluate the effects on concentrations of milk urea and rumen ammonia, urinary output, and drinking water intake. The treatments were achieved by K supplementation on top of a low-K basal ration fed at individual allowances fixed throughout the experiment. The basal ration, consumed at 20.2 kg of dry matter (DM)/d, provided 165 g of crude protein/kg of DM and consisted of grass silage, concentrates, and urea in the proportions 39.3:60.0:0.7 on a DM basis. Potassium bicarbonate supplementation was 0, 616, and 1,142 g/d, respectively, to give total ration K concentrations that were low (LO; 12 g/kg of DM), medium (MED; 23 g/kg of DM), or high (HI; 32 g/kg of DM). Production and composition of milk was not affected by treatment. A linear effect on milk urea concentration was detected, being 4.48, 4.18, and 3.77 mM for LO, MED, and HI, respectively, and a linear tendency for rumen ammonia concentration with 6.65, 6.51, and 5.84 mg of NH₃-N/dL for LO, MED, and HI, respectively. Milk urea concentration peaked about 3 h after the rumen ammonia peak from the morning feeding, at a level 1.3 mM over the baseline. Urinary urea excretion declined linearly (105, 103, and 98 g of urea-N/d for LO, MED, and HI, respectively). Linear increases occurred in urinary output (0.058 ± 0.001 kg of urine/g of K intake; no intercept; coefficient of determination = 0.997) and drinking water intake (65.9 ± 2.02 + 0.069 ± 0.004 kg of water/g of K intake; coefficient of determination = 0.95). Urinary K concentration leveled off at 12.4 g/L. Urinary creatinine excretion was not affected by K addition, but allantoin excretion increased linearly by 27% from LO to HI, suggesting increased rumen microbial growth. Rumen pH, acetate proportion of total volatile fatty acids, and digestibility of DM, organic matter, and neutral detergent fiber increased linearly with increasing potassium intake. We concluded that increased ration K concentration lowers milk urea concentration with a magnitude significant for the interpretation of milk urea values, but other sources of variation, such as sampling time relative to feeding, may be even more important.     

Exploration and exploitation in project-based organizations: Development and diffusion of knowledge at different organizational levels in construction companies

Management studies highlight the importance of an organization's capability to both exploit existing knowledge and technologies for short-term profits and also explore new knowledge and technologies to enhance long-term innovation. Although this paradox recently has received escalating interest in management research, studies dealing with project-levels and project-based organizations (PBOs) are scarce. This conceptual paper discusses how PBOs in the construction industry can manage the exploration/exploitation paradox at different organizational levels. Short-term project focus and decentralization inhibits learning from one point in time and space to another, making it easier to reap the benefits of exploitation than of exploration. Current structural and sequential separation of exploration and exploitation activities at business unit, project portfolio, and project levels do not solve the paradox, due to lack of integrating mechanisms. Hence, PBOs in the construction industry may suffer from inadequate extent of exploration, while the extent of exploitation is not reaching its potential. Cooperative procurement procedures can serve as a basis for facilitating both exploration and exploitation of knowledge and technologies in construction projects.     

Theory of He trapping, diffusion, and clustering in UO2

We have performed ab initio total energy calculations to investigate the behavior of helium and its diffusion properties in uranium dioxide (UO₂). Our investigations are based on the density functional theory within the generalized gradient approximation (GGA). The trapping behavior of He in UO₂ has been modeled with a supercell containing 96-atoms as well as uranium and oxygen vacancy trapping sites. The calculated incorporation energies show that for He a uranium vacancy is more stable than an oxygen vacancy or an octahedral interstitial site (OIS). Interstitial site hopping is found to be the rate-determining mechanism of the He diffusion process and the corresponding migration energy is computed as 2.79 eV at 0 K (with the spin-orbit coupling (SOC) included), and as 2.09 eV by using the thermally expanded lattice parameter of UO₂ at 1200 K, which is relatively close to the experimental value of 2.0 eV. The lattice expansion coefficient of He-induced swelling of UO₂ is calculated as 9 × 10⁻². For two He atoms, we have found that they form a dumbbell configuration if they are close enough to each other, and that the lattice expansion induced by a dumbbell is larger than by two distant interstitial He atoms. The clustering tendency of He has been studied for small clusters of up to six He atoms. We find that He strongly tends to cluster in the vicinity of an OIS, and that the collective action of the He atoms is sufficient to spontaneously create additional point defects around the He cluster in the UO₂ lattice.