On the structure and logic of typical material flow systems†

A queueing network technique (Solberg's CAN-Q) and a flow control simulator (SINDECS) are applied to investigate general, fundamental performance properties of material flow systems (MFS). The effects of a system's structure and flow logic on performance are compared for three typical flow systems: transfer line, recirculating conveyor loop, and job shop. The concepts of Most Economical MFS for a given performance level, Iso-Performance MTS combinations, and Overall MFS Configuration Measures are introduced.     

On the preparation and application of novel PVDF–POSS systems

Novel systems based on poly(vinylidene fluoride) (PVDF) and polyhedral oligomeric silsesquioxane (POSS) have been prepared by grafting amino-containing POSS (POSS–NH₂) onto the surface of modified PVDF (PVDFm). Namely, the approach consists of a preliminary modification of PVDF by a chemical treatment with an alkaline solution, in order to obtain unsaturations, and a subsequent surface reaction of PVDFm with POSS molecules characterized by an amino group as reactive side. The level of polymer unsaturation, measured by Raman spectroscopy, turned out to be finely tuned by varying the dehydrofluorination reaction time. The surface grafting of POSS has been studied by SEM-EDS analysis, Raman and XPS spectroscopy. Indeed, while the level of modification of PVDFm has been found to decrease as a consequence of the reaction with POSS, thus indicating a likely saturation of double bonds by silsequioxane molecules, the Si concentration turned out to increase with increasing the concentration of the polymer surface unsaturation. The feasibility of the application of POSS grafting onto the surface of membranes, based on PVDFm, has also been verified.     

On the analogy between the evolution of thermodynamic and bibliometric systems: a breakthrough or just a bubble?

This paper presents an in depth study of an interesting analogy, recently proposed by Prathap (Scientometrics 87(3):515–524, 2011a), between the evolution of thermodynamic and bibliometric systems. The goal is to highlight some weaknesses and clarify some “dark sides” in the conceptual framework of this analogy, discussing the formal validity and practical meaning of the concepts of Energy, Exergy and Entropy in bibliometrics. Specifically, this analogy highlights the following major criticalities: (1) the definitions of E and X are controversial, (2) the equivalence classes of E and X are questionable, (3) the parallel between the evolution of thermodynamic and bibliometric systems is forced, (4) X is a non-monotonic performance indicator, and (5) in bibliometrics the condition of “thermodynamic perfection” is questionable. Argument is supported by many analytical demonstrations and practical examples.     

On the Freezing and Melting Behavior of the Eutectic Pt?CC

The feasibility of referring to freezing as an alternative to melting for defining the eutectic transition temperature has been studied using two Pt?CC cells constructed at NIM, one of a sleeve type, and the other of a hybrid type, including support. Freezing and melting experiments have been done by varying the offset of the furnace temperature T _furn with respect to the nominal eutectic temperature T _E used to freeze the fixed point with offsets (T _furn?T _E)_freeze from ?5 K to ?40 K, followed by melting at a fixed offset (T _furn?T _E)_melt =?+?20 K. Plotting the liquidus temperatures T _liq,freeze and T _liq,melt obtained for freezing and melting against ${(T_{\rm E}-T_{\rm furn})^{1/2}_{\rm freeze}}$ resulted in linear relations for both cells, allowing extrapolation toward T _liq,freeze(0) and T _{liq, melt}(0). For the cells Pt?CC5# and Pt?CC6# under study: T _liq,melt(0)?T _liq,freeze(0) =?10 mK and 20 mK, respectively, with a standard uncertainty of 30 mK for both T _liq,melt(0) and T _liq,freeze(0). The coherence of the results obtained for melting and freezing indicates that freezing can be used, as an alternative to melting, to define the liquidus temperature T _liq(0) of the eutectic Pt?CC.     

On the shoulders of students? The contribution of PhD students to the advancement of knowledge

Using the participation in peer reviewed publications of all doctoral students in Quebec over the 2000–2007 period, this paper provides the first large scale analysis of their research effort. It shows that PhD students contribute to about a third of the publication output of the province, with doctoral students in the natural and medical sciences being present in a higher proportion of papers published than their colleagues of the social sciences and humanities. Collaboration is an important component of this socialization: disciplines in which student collaboration is higher are also those in which doctoral students are the most involved in peer-reviewed publications. In terms of scientific impact, papers co-signed by doctorate students obtain significantly lower citation rates than other Quebec papers, except in natural sciences and engineering. Finally, this paper shows that involving doctoral students in publications is positively linked with degree completion and ulterior career in research.     

Exploring the phenomenon of company-specific production systems: one-best-way or own-best-way?

This explorative study investigates the phenomenon of the company-specific production system (XPS). It has been a strong and recent trend across many manufacturing industries to develop and deploy such a corporate improvement programme. Five propositions regarding the uniqueness of XPSs are derived from universalistic versus contingent perspectives on improvement programmes. The main XPS principles of 30 renowned multinationals are analysed for similarities and differences. In conclusion, XPSs largely represent variants of the same in content. They represent an own-best-way approach to the one-best-way paradigm. Even though a tight relationship to the Toyota Production System (TPS) and lean production is established, the findings raise a red flag that XPSs might suffer under a too rigid, path-dependent development process from what has become an overly technical understanding of the TPS. This study also questions whether modern manufacturers have sufficiently integrated other essential elements of modern operations such as the use of ERP, automation and real-time response technologies in their XPSs. These findings have direct implications for practitioners and provide interesting opportunities for further research.     

On the stability of uncertain homogeneous bilinear systems subjected to time‐delay and constrained inputs

Abstract

This paper addresses the stability test problem for homogeneous bilinear uncertain time‐delay systems with constrained inputs. By using differential inequality, some sufficient criteria are presented to guarantee the asymptotic stability of overall systems. Furthermore, the transient behaviors of the mentioned systems are also estimated.     

On the application of the “rule of mixture” to microhardness of complex polymer systems containing a soft component and/or phase

The main goal of this work is to find a reasonable explanation for the frequently reported drastic deviations from the “rule of mixture” applied for calculation of the overall microhardness, H, of complex polymer systems comprising a soft, (with a glass transition, T _g, or melting, T _m, temperatures below room temperature) component and/or phase. According to the common practice, the contribution to H of the soft component and/or phase, H ^s, is considered as H ^s = 0, which results in extremely large differences between the measured and calculated H values for systems comprising more than 20–25 wt% soft component and/or phase. For such systems a different deformation mechanism during indentation process is postulated, namely “floating” of the solid particles in the soft component and/or phase, in addition to their plastic deformation. The contribution of the “floating effect” to the overall H is accounted for by the empirically derived relationship H = 1.97 T _g−571. Using the reported data on H and T _g for homopolymers, blockcopolymers and blends, the H values are recalculated and a good agreement with the experimentally measured values is found. A modified additivity law is suggested, which contains a term accounting for the contribution of the soft component and/or phase to the overall microhardness via the relationship between H and T _g; its application results in much smaller differences between the measured and calculated H values. On leave from Laboratory on Polymers, University of Sofia, 1126 Sofia, Bulgaria.     

On the mechanism of the Ranque–Hilsch effect

A model of flow in a Ranque vortex tube is suggested. It is based not on the thermal interaction between hot and cold flows, but rather on a mechanical one. It is shown that to describe the Ranque–Hilsch effect it is necessary, along with the radial flow, to take into account the uptake or addition of mass, as well as to ensure a smoother conjugation between a forced and a peripheral vortices, demanding the continuity not only of the tangential velocity component, but also of its first derivative with respect to the radius. In this case, the motion in the vortex tube is considered as a system of vortex flows and vortex sources interacting between themselves.     

On the Origin of the δk-Model and the Model of Plastic Strips

On the basis of a survey of works, we demonstrate the priority of the Lviv school of mechanics in the field of creation and development of the deformation theory of limiting equilibrium of bodies with cracks known as the _k -model. The theory is based on the criterion of crack opening displacement proposed by Leonov and Panasyuk and on the procedure of evaluation of this quantity by modeling the inelastic zones in front of the crack by cuts the edges of which are loaded by certain stresses ₀ whose physical meaning is determined by the properties of the material. This method (known as the model of plastic strips) is also used for the determination of the development of plastic zones at the crack tip for various configurations of plates and loads and also in twisted bodies. The results of numerical calculations agree with the experimental data.     

On the transformations of the ψ-AlCuFe icosahedral phase

In the present investigation, different alloy compositions close to the ternary composition values, where the icosahedral phase in AlFeCu is obtained, have been studied. The specimens were obtained using a rapid solidification technique with subsequent thermal treatments of 600°C, 700°C, 800°C and 900°C. The obtained specimens were characterized with X-ray diffraction patterns (XRD) and transmission electron microscopy (TEM). The experimental results show different transformations of the icosahedral phase to crystalline phases between 800°C and 700°C .The cubic β-phase is a solid solution which regulates the formation and decomposition of the ψ-Al₆Cu₂Fe phase to different crystalline phases such as the tetragonal (Al₇Cu₂Fe) and monoclinic (Al₁₃Fe₄) phases.     

On the theory of superfluidity of helium II near the λ point

The present state of the theory of superfluidity of helium II near the point is reviewed. The basic assumptions underlying this theory and the limits of its applicability are discussed. The results of the solution of some problems in the framework of the theory are presented and compared with experimental data. The necessity and possibility of further comparison of the theory with experiment are emphasized.     

On the definition of the ‘Best’ confidence interval

The definition of a confidence interval used in risk and reliability calculations is not the best one because it does not define the shortest confidence interval for skew distributions. In this paper the definition of the cumulative distribution was generalized by using Lebesgue integration. The application of a new definition allows the introduction of the shortest confidence interval (or domain) for all cases.     

Increasing the efficiency of systems for the detection of the contours of parts on the basis of Hough’s transformation

Hough’s transformation, which is used in systems for the detection and control of the geometric parameters of parts, along with the complex influence of different sets of filters in a contour detection system are considered. The basic methods of filtration that promote suppression of noise, the elimination of false contours, tapering of the edges of contours, and the removal of residual noise in the form of unconnected points of a contour are described. A quantitative estimate of the efficiency gained with the use of these filters is given from the results of tests.     

Does the concept of safety culture help or hinder systems thinking in safety?

The concept of safety culture has become established in safety management applications in all major safety-critical domains. The idea that safety culture somehow represents a “systemic view” on safety is seldom explicitly spoken out, but nevertheless seem to linger behind many safety culture discourses. However, in this paper we argue that the “new” contribution to safety management from safety culture never really became integrated with classical engineering principles and concepts. This integration would have been necessary for the development of a more genuine systems-oriented view on safety; e.g. a conception of safety in which human, technological, organisational and cultural factors are understood as mutually interacting elements. Without of this integration, researchers and the users of the various tools and methods associated with safety culture have sometimes fostered a belief that “safety culture” in fact represents such a systemic view about safety. This belief is, however, not backed up by theoretical or empirical evidence. It is true that safety culture, at least in some sense, represents a holistic term—a totality of factors that include human, organisational and technological aspects. However, the departure for such safety culture models is still human and organisational factors rather than technology (or safety) itself. The aim of this paper is to critically review the various uses of the concept of safety culture as representing a systemic view on safety. The article will take a look at the concepts of culture and safety culture based on previous studies, and outlines in more detail the theoretical challenges in safety culture as a systems concept. The paper also presents recommendations on how to make safety culture more systemic.     

On the Correction of the Melting Curve of the Eutectic Co–C for the Effect of the Thermal Inertia of the Furnace

This paper considers the influence of the thermal inertia of the furnace on the shape of the melting curve of the eutectic Co–C. To this end, melting experiments have been performed in a uniform three-zone furnace, with an inherent substantial thermal inertia. The thermal inertia has been quantified by measuring the step-response of the furnace with the sample in its solid state, just below its melting temperature. From the analysis of the effect of the thermal inertia of the furnace, it turned out that during melting the temperature distribution within the furnace, surrounding the crucible, is bound to be in a non-stationary state. This provided the key to properly finalizing the correction to be applied. The shape of the corrected curve differs considerably from that of the curve, as measured, in that the former shows a flatter melting plateau, and a larger curvature on the way down to the solidus point. As regards the liquidus temperature \(T_{\mathrm{liq}}\)—of major interest in the characterization of the transition temperature of high-temperature fixed points—it is demonstrated that the thermal inertia of the furnace shows a kind of self-compensating mechanism. But the effects of the thermal inertia of the furnace on the parameters defining the Scheil fit, involved in the correction procedure, were considerable.     

Charge carrier lifetime recovery in γ-irradiated silicon under the action of ultrasound

Ultrasonic treatment of ??-irradiated silicon can lead to a significant (up to about 70%) recovery of the minority carrier lifetime reduced by the irradiation. A mechanism of the ultrasound-induced recovery is proposed, which is based on the release of vacancies from E-type centers followed by their trapping on defect sinks. It is suggested that the role of defect sinks can be played by A-type microdefects.     

On the Formability of Some Metastable Alloy Phases

Pattern recognition and neural network methods have been used to investigate the formability of metastable alloy phases, It has been found that some chemi cal bond parameters Such as valence electron number, electronegativity and metallic radii of cor-nponent elements are the dominating fac tors affecting metastable alloy phase formation. Some semi-empirical rules found in this way may be useful for the construction of expert system for materials design.     

Publication attributes of leadership: what do they mean?

The article evaluates 48 approaches to leadership for the first time for the period of 1965–2016 using bibliometric methods. Our analysis combines four parameters: the number of publications, citations, self-citations, and dispersion of literature (a new parameter). The question of what is the most influential approach to leadership is addressed. We argue that the interplay among the four attributes observed in this study shows that transformational leadership is the most influential and popular approach to leadership in leadership studies today. However, there is a question of whether the excessive self-citations in this approach to leadership play a role in its augmented visibility.