Stabilization of artificial gas-lift process using nonlinear predictive generalized minimum variance control

Artificial gas-lift (AGL) is one of the most widely used methods in oil production to maintain acceptable oil flow to the processing equipment and sales when the reservoir pressure is not high enough. In spite of its popularity, the AGL process is prone to casing-heading instability, which is revealed as significant flow oscillation. This is undesirable as it results in production losses and unstable behavior that has negative impact on the downstream equipment. Controller design for such a process is very challenging as it exhibits highly nonlinear dynamics. In this work, the predictive generalized minimum variance control (NPGMV) is employed to derive a robust controller based on the state estimation to stabilize AGL process when casing-heading phenomenon occurs. A closed-form optimal control law is obtained based on the Taylor series approximation. Further, a nonlinear state observer is produced and combined with the controller to ensure closed-loop control through variables that are most beneficial to the system performance, which are unmeasurable and can be obtained only via estimation. Through simulation studies, the effectiveness of the proposed controller is demonstrated.     

Analysis of orbital stability in lure system,based on dynamic harmonic balance

A criterion of orbital stability of a limit cycle in a Lure system is formulated using the dynamic harmonic balance (DHB) principle and the describing function (DF) method. It is demonstrated that a more precise formulation of orbital stability than that provided by the Loeb's criterion can be produced. This enhancement is achieved through elimination of the assumption that is used in Loeb's criterion derivation. It is demonstrated in the paper that this assumption does not hold. An example of analysis is given.     

The Evolution of the Concept of Capacitance Throughout the Development of the Electric Theory and the Understanding of Its Meaning by University Students

There are few didactic studies concerning the difficulties met by students inunderstanding the meaning of capacitance in a charged body. However, theunderstanding of capacitance can be a good indicator of the Students' learningof electrostatic theory in general. To describe Students' difficulties in learningthis concept we have considered, on the one hand, that individuals constructmental representations in order to help their understanding of the way a physicalsystem works under varied circumstances. On the other hand, a critical study ofthe history and epistemology of science is likely to enlighten us teachers andresearchers about the presence of qualitative leaps in the evolution of a concept.Thus, the consideration by teachers of these `discontinuities between meaningsfor the same concept, may lead them to understand Students' difficulties on learningit. We developed a historical study of the development of the capacitance conceptand an empirical study with students to identify historical and learning difficulties.The results obtained seem to show that most of the students who reason aboutaspects related to the charge of bodies and capacitance feel more comfortablewhen they talk in terms of charge than in terms of electric potential in a similarway to the first explanations of the early electric theories.     

Teaching OO Software Engineering by Example: The Games Factory

Object‐oriented analysis, design, and programming is a software development technology which has attracted universal attention in the past few years. We do not think that object‐oriented technology is a completely new approach to software construction; it is merely the consequent continuation of software engineering principles which have evolved since 1968, the year of the birth of software engineering. This article describes a course on software engineering with objects which track the evolution of this discipline. We work through the history of these concepts using a single application domain, demonstrating how the relevant analysis and design methods evolved over time, culminating in object‐oriented techniques.     

Post-Soviet science: Difficulties in the transformation of the R&D systems in Russia and Ukraine

In the late 1980s, the Soviet Union was among the foremost leaders of world science, thanks in large part to its heavy involvement in military programmes. The USSR developed a large research infrastructure but it lacked effective mechanisms for the commercialization of research results. The main aim of the transformation of R&D systems in the post-Soviet states in the 1990s and early 2000s was the re-orientation of scientific activities away from military and towards civilian goals. Analysis of statistical data at the macro-level suggests that this attempt was not particularly successful. Indeed, most newly independent states could not even preserve a ‘critical mass’ of scientific activities in order to remain among the list of significant producers of research results. In the post-Soviet countries (and in this paper we focus on Russia and Ukraine as the largest states of the region), inputs from the R&D system have failed to generate wealth-creating outputs because of a systemic inability to use the resources for generating commercially viable results effectively. All post-Soviet countries, including Russia and Ukraine, urgently need not only a major transformation within the R&D system, but also important changes in the wider ‘environment’. It is important to stress that, in recent years, changes in R&D have been determined not only by the general economic situation itself but also by the general policy of the post-Soviet states. While Russia has expressed ambitions to regain its former influence as a great power and to use S&T to achieve this goal, Ukraine has no clearly determined objectives for the development of its national science system. However, both countries face certain common problems. The development of relevant institutes and the stimulation of demand for R&D results from the side of industry, broader involvement in the international division of scientific work, and the introduction of adequate legal protection for intellectual property rights are all of critical importance for S&T institutes and other research organizations in Russia and Ukraine. This paper shows that the reforms in the R&D sector have been relatively modest and rather unsystematic over the last one and a half decades. The key challenges, which relate to the inertia and the negative aspects of the previous period (for example, a extremely low level of replacement of aging manpower, largely outdated scientific equipment in research laboratories, and institutional mechanisms that are not relevant to the market economy), pose serious problems for the transformation of the R&D systems in both countries, despite new possibilities and a willingness to increase financial support for R&D.     

Topological metrics in academic genealogy graphs

Academic genealogy aims to structure and analyze the mentoring relationships between advisor and advisee. The representation of this structure results in academic genealogy graphs. For the analysis and characterization of these graphs, we present a set of metrics and their corresponding mirror metrics that capture the characteristics of its topological structure and represent them as quantitative attributes. The metrics of fecundity, fertility, descendants, cousins, generations, and relationships consider the descendants of the academics represented in the graph. The mirror metric of these topological metrics considers the ascendancy of academics. Individually, the metrics have strong semantic intuition and define characteristics regarding the performance in the mentoring of an academic. Together, the metrics are useful for the identification, characterization, and classification of communities and their members. The genealogical data available through the platforms of the Mathematics Genealogy Project and the Academic Family Tree were used as case studies. Two hundred thirteen thousand and 675,000 academic records were obtained for each project. We analyze the capacity of characterization of the metrics using the structuring of a similarity graph and through the distribution of the nodes in principal components. We observed that the set of metrics is capable of capturing the configuration pattern existing in genealogy graphs independently of its scale.     

Comparison of the force-, velocity-, and power-time curves recorded with a force plate and a linear velocity transducer

This study aimed to correlate, compare, and determine the reliability of force, velocity, and power values collected with a force plate (FP) and a linear transducer during loaded jumps. Twenty-three swimmers performed an incremental loading test at 25, 50, 75, and 100% of their own body weight on a FP. A linear velocity transducer (LVT) was attached to the bar to assess the peak and the mean values of force, velocity, and power. Both the peak variables (r = 0.94 – 0.99 for peak force, r = 0.83 – 0.91 for peak velocity, and r = 0.90–0.94 for peak power; p < 0.001) and the mean variables (r = 0.96–0.99 for mean force, r = 0.87–0.89 for mean velocity, and r = 0.93–0.96 for mean power; p < 0.001) were strongly correlated between both measurement tools. Differences in the shape of the force-, velocity-, and power-time curves were observed. The LVT data showed a steeper increase in these variables at the beginning of the movement, while the FP recorded larger values in the latter part. Peak values were more reliable than mean values. These results suggest that the LVT is a valid tool for the assessment of loaded squat jump.