Aboveground nitrogen in relation to estimated total plant uptake in maize and bean

The main objective of this field study was to estimate the total plant uptake of soil mineral N in maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) grown in crop rotations under different N content in Nicaragua. Secondary objectives were to estimate the fraction of the measured soil mineral N content taken up in this way, and to determine how the measured N in plant aboveground parts was related to the total mineral N uptake. A large variation in N content was obtained by using data from fertilisation experiments. Plant total N uptake was estimated as the residual N in a mass balance calculation of soil mineral N. Mineral N content in the top 0–0.3 m soil layer in the field cultivations and in tubes isolated from root uptake, and N content in aboveground plant parts were measured every 30 days. Estimated plant total uptake of soil mineral N varied considerably (2.5–14 g N m⁻² 30 day⁻¹) over periods and N treatments. The range of variation was similar for maize and bean. The fraction of the soil mineral N that was taken up by the plant daily varied more in maize (about 0.03–0.12 day⁻¹) than in bean (about 0.05–0.08 day⁻¹). Our results suggest that monthly changes in N in aboveground plant parts were linearly related to plant total N uptake during the same period. Aboveground plant N constituted between about 55% and 80% of total uptake of soil mineral N in maize depending on period within season, whereas for bean it was more constant and smaller (about 40%).     

Engineering Analysis and Design with ALE-VMS and Space–Time Methods

Flow problems with moving boundaries and interfaces include fluid–structure interaction (FSI) and a number of other classes of problems, have an important place in engineering analysis and design, and offer some formidable computational challenges. Bringing solution and analysis to them motivated the Deforming-Spatial-Domain/Stabilized Space–Time (DSD/SST) method and also the variational multiscale version of the Arbitrary Lagrangian–Eulerian method (ALE-VMS). Since their inception, these two methods and their improved versions have been applied to a diverse set of challenging problems with a common core computational technology need. The classes of problems solved include free-surface and two-fluid flows, fluid–object and fluid–particle interaction, FSI, and flows with solid surfaces in fast, linear or rotational relative motion. Some of the most challenging FSI problems, including parachute FSI, wind-turbine FSI and arterial FSI, are being solved and analyzed with the DSD/SST and ALE-VMS methods as core technologies. Better accuracy and improved turbulence modeling were brought with the recently-introduced VMS version of the DSD/SST method, which is called DSD/SST-VMST (also ST-VMS). In specific classes of problems, such as parachute FSI, arterial FSI, ship hydrodynamics, fluid–object interaction, aerodynamics of flapping wings, and wind-turbine aerodynamics and FSI, the scope and accuracy of the FSI modeling were increased with the special ALE-VMS and ST FSI techniques targeting each of those classes of problems. This article provides an overview of the core ALE-VMS and ST FSI techniques, their recent versions, and the special ALE-VMS and ST FSI techniques. It also provides examples of challenging problems solved and analyzed in parachute FSI, arterial FSI, ship hydrodynamics, aerodynamics of flapping wings, wind-turbine aerodynamics, and bridge-deck aerodynamics and vortex-induced vibrations.     

Persistent problems and practices in information systems development: a study of mobile applications development and distribution

The widespread uptake of mobile technologies has witnessed a re‐structuring of the mobile market with major shifts in the predominance of particular firms and the emergence of new business models. These sociotechnical trends are significant in the ways that they are influencing and shaping the working lives of software professionals. Building on prior research investigating the persistent problems and practices of systems development, this paper examines mobile applications development and distribution. A qualitative study of 60 developers based in Sweden, the UK and the USA was analysed around the interrelated problems of diversity, knowledge and structure. The analysis revealed how platform‐based development in an evolving mobile market represents significant changes at the business environment level. These changes ripple through and accentuate ongoing trends and developments, intensifying the persistent problems and challenges facing software developers.     

Oxidative dehydrogenation of ethane on Pt–Sn impregnated monoliths

The oxidative dehydrogenation of ethane was studied over Pt–Sn impregnated monoliths at 1 bar, 600–900 °C and with different contents of oxygen, hydrogen and steam in the feed gas. As expected a decrease in oxygen in the feed led to a decrease in the conversion of ethane due to lower temperatures in the reactor. Adding steam to the feed showed no effect on the ethane conversion or the ethene selectivity. When the hydrogen/ethane ratio in the feed was varied from 0 to 0.5 at 700 and 850 °C, it resulted in a significant increase in the selectivity to ethene while the ethane conversion remained relatively unchanged. At 700 °C the selectivity increased from about 50% to 93% (carbon basis) with only a small decrease in the conversion of ethane. The results clearly show that both Pt and Sn have a catalytic effect. Pt caused the ethane conversion to rise and addition of Sn resulted in much better ethene selectivity. However, even though Sn alone showed some catalytic effect at lower temperatures, it cannot explain the great difference between the Pt and Pt–Sn catalysts. A reasonable assumption is therefore that there exist interactions between Pt and Sn that gives the Pt–Sn catalysts excellent properties for oxidative dehydrogenation of ethane, in particular upon addition of hydrogen.     

On hypercube packings,blocking sets and a covering problem

Consider sets S of hypercubes of side 2 in the discrete n-dimensional torus of side 4 with the property that every possible hypercube of side 2 has a nonempty intersection with some hypercube in S. The problem of minimizing the size of S is studied in two settings, depending on whether intersections between hypercubes in S are allowed or not. If intersections are not allowed, then one is asking for the smallest size of a non-extensible packing S  ; this size is denoted by f(n)$f(n)$. If intersections are allowed, then the structure S is called a blocking set. The smallest size of a blocking set S   is denoted by h(n)$h(n)$. By computer-aided techniques, it is shown that f(5)=12$f(5)=12$, f(6)=16$f(6)=16$, h(6)=15$h(6)=15$ and h(7)≤23$h(7)\le 23$. Also, non-extensible packings as well as blocking sets of certain small sizes are classified for n≤6$n\le 6$. There is a direct connection between these problems and a covering problem originating from the football pools.     

Response surface single loop reliability-based design optimization with higher-order reliability assessment

Reliability-based design optimization (RBDO) aims at determination of the optimal design in the presence of uncertainty. The available Single-Loop approaches for RBDO are based on the First-Order Reliability Method (FORM) for the computation of the probability of failure, along with different approximations in order to avoid the expensive inner loop aiming at finding the Most Probable Point (MPP). However, the use of FORM in RBDO may not lead to sufficient accuracy depending on the degree of nonlinearity of the limit-state function. This is demonstrated for an extensively studied reliability-based design for vehicle crashworthiness problem solved in this paper, where all RBDO methods based on FORM strongly violates the probabilistic constraints. The Response Surface Single Loop (RSSL) method for RBDO is proposed based on the higher order probability computation for quadratic models previously presented by the authors. The RSSL-method bypasses the concept of an MPP and has high accuracy and efficiency. The method can solve problems with both constant and varying standard deviation of design variables and is particularly well suited for typical industrial applications where general quadratic response surface models can be used. If the quadratic response surface models of the deterministic constraints are valid in the whole region of interest, the method becomes a true single loop method with accuracy higher than traditional SORM. In other cases, quadratic response surface models are fitted to the deterministic constraints around the deterministic solution and the RBDO problem is solved using the proposed single loop method.     

Realization strategies of dedicated path protection: A bandwidth cost perspective

Communication networks have to provide a high level of availability and instantaneous recovery after failures in order to ensure sufficient survivability for mission-critical services. Currently, dedicated path protection (or 1 + 1) is implemented in backbone networks to provide the necessary resilience and instantaneous recovery against single link failures with remarkable simplicity. However, in order to satisfy strict availability requirements, connections also have to be resilient against Shared Risk Link Group (SRLG) failures. In addition, switching matrix reconfigurations have to be avoided after a failure in order to guarantee instantaneous recovery. For this purpose, there are several possible realization strategies improving the characteristics of traditional 1 + 1 path protection by lowering reserved bandwidth while conserving all its favorable properties. These methods either utilize diversity coding, network coding, or generalize the disjoint-path constraint of 1 + 1.In this paper, we consider the cost aspect of the traditional and the alternative 1 + 1 realization strategies. We evaluate the bandwidth cost of different schemes both analytically and empirically in realistic network topologies. As the more complex realizations lead to NP-complete problems even in the single link failure case, we propose both Integer Linear Programming (ILP) based optimal methods, as well as heuristic and meta-heuristic approaches to solve them. Our findings provide a tool and guidelines for service providers for selecting the path protection method with the lowest bandwidth cost for their network corresponding to a given level of reliability.     

An Empirical Study on Views of Importance of Change Impact Analysis Issues

Change impact analysis is a change management activity that previously has been studied much from a technical perspective. For example, much work focuses on methods for determining the impact of a change. In this paper, we present results from a study on the role of impact analysis in the change management process. In the study, impact analysis issues were prioritised with respect to criticality by software professionals from an organisational perspective and a self-perspective. The software professionals belonged to three organisational levels: operative, tactical and strategic. Qualitative and statistical analyses with respect to differences between perspectives as well as levels are presented. The results show that important issues for a particular level are tightly related to how the level is defined. Similarly, issues important from an organisational perspective are more holistic than those important from a self-perspective. However, our data indicate that the self-perspective colours the organisational perspective, meaning that personal opinions and attitudes cannot easily be disregarded. In comparing the perspectives and the levels, we visualise the differences in a way that allow us to discuss two classes of issues: high-priority and medium-priority. The most important issues from this point of view concern fundamental aspects of impact analysis and its execution.