Betweenness and diversity in journal citation networks as measures of interdisciplinarity—A tribute to Eugene Garfield

Journals were central to Eugene Garfield’s research interests. Among other things, journals are considered as units of analysis for bibliographic databases such as the Web of Science and Scopus. In addition to providing a basis for disciplinary classifications of journals, journal citation patterns span networks across boundaries to variable extents. Using betweenness centrality (BC) and diversity, we elaborate on the question of how to distinguish and rank journals in terms of interdisciplinarity. Interdisciplinarity, however, is difficult to operationalize in the absence of an operational definition of disciplines; the diversity of a unit of analysis is sample-dependent. BC can be considered as a measure of multi-disciplinarity. Diversity of co-citation in a citing document has been considered as an indicator of knowledge integration, but an author can also generate trans-disciplinary—that is, non-disciplined—variation by citing sources from other disciplines. Diversity in the bibliographic coupling among citing documents can analogously be considered as diffusion  or differentiation of knowledge across disciplines. Because the citation networks in the cited direction reflect both structure and variation, diversity in this direction is perhaps the best available measure of interdisciplinarity at the journal level. Furthermore, diversity is based on a summation and can therefore be decomposed; differences among (sub)sets can be tested for statistical significance. In the appendix, a general-purpose routine for measuring diversity in networks is provided.     

Fatigue of metals – What the designer needs?

Engineering designers have to tackle various fatigue problems in their routine work. Some problems are simple and other are complex. Most of the designers have been taught only a small part of the suitable fatigue knowledge needed to successfully deal with many of these problems except for the most trivial ones. The main reason is the vast amount and complexity of the fatigue discipline, and lack of a clear integrated approach to the main fatigue problems that may be conveniently utilized by designers. An integrated approach to fatigue, that has been introduced by one of the authors in the past, is here extended, simplified and proposed as a comprehensive fatigue design tool for engineers. The whole fatigue domain is divided into six zones that include different fatigue regimes. The propagating crack length is considered as the sole parameter to evaluate safe fatigue life, including the use of an “equivalent crack propagation rate”, which averages the intense variations of CPR in the vicinity of grain boundaries. Contrary to the many unified relations to evaluate fatigue crack propagation that were proposed in the past, the current study is based on separation. For each fatigue zone a unique prediction relation is presented. Flow chart of comprehensive software for calculation of crack propagation in the whole fatigue domain is explained, and simulation results show good fit to published test results. The method is claimed to fit for use mainly by design engineers, but possibly by fatigue experts as well.     

Fatigue crack propagation work coefficient—a material constant giving degree of resistance to fatigue crack growth

Study on fatigue crack growth in steels was carried out from energetic point of view, i.e. taking account of plastic work around the fatigue crack. Based on the examination of the relation between fatigue crack growth rate (da/dN) and the plastic work around the fatigue crack tip (W_0.02 in SUS304, Fe-3Si and HT 60 steels, a material constant-fatigue crack propagation work coefficient-Q_0.02 is proposed. It is the ratio of W_0.02 to da/dN and means the degree of the resistance to fatigue crack growth. Numerical expression of Q_0.02 by mechanical properties was derived, which is given by

$\text{Q}{}_{0.02}\text{=}\text{9.3x10}{}^1\text{(σ}{}_{\mathrm{y}}\text{+σ}{}_{0.2}\text{)}\text{σ}{}_{\mathrm{y}}{}^{1.3}$

Comparison of Q_0.02 of various steels showed that Q_0.02 of high strength steels is very small compared with that of low strength steels. Graphical representation of the relation between Q_0.02 and da/dN at various values of ΔK/σ_y for steels revealed that da/dN at given value of ΔK/σ_y increase with decreasing Q_0.02. It is shown that fatigue crack growth behaviour of a steel (da/dN-ΔK relation) can be obtained from the Q_0.02-da/dN diagram by knowing the mechanical properties. Discussion on design stress level of the steels is also given.     

The Lymphocyte Story – an Overview of Selected Highlights on the in Vitro Activation of Human Lymphocytes in Space

Since the first flight of humans into space it is known that space flight affects the immune system; especially a weakening of the reactivity of T-lymphocytes after flight has been observed. In an in vitro experiment, proposed by Augusto Cogoli and flown in Spacelab-1 in 1983, the activation of T-lymphocytes was found to be strongly inhibited in microgravity. This surprising result triggered extended investigations in space and on the ground by us and other research teams. T-cells are that subpopulation of lymphocytes responsible for the activation of the specific immune system. The mechanism of T-cell activation is very complex; 3 different signals are required as well as an interaction between T-lymphocytes and monocytes. Cell motility based on a continuous rearrangement of the cytoskeletal network within the cell is essential for cell-cell contacts. The objective of all our experiments performed on different platforms in space as well as in simulated microgravity on ground was to understand and explain the dysfunction of the cell activation under reduced gravity conditions. On sounding rockets we have studied the influence of microgravity on the delivery of the first signal, the motility of lymphocytes as well as changes in the cytoskeletal structure and early gene expression. On long term missions we investigated many aspects of the delivery of the 2 ^nd and 3 ^rd signal, including motility and aggregate formation of lymphocytes, interaction of lymphocytes with monocytes, motility of monocytes and changes in different cytoskeletal structures.     

Mathematical and physical aspects of material failure: A tribute to Jean-Baptiste Leblond’s odyssey in fracture mechanics

International Journal of Fracture -     

Fatigue of brittle materials—A critical appraisal

Recent demands for high performance ceramics and glass for various applications from bioceramics to cutting tools under fluctuating stress conditions has focussed attention of the scientific community towards fatigue behaviour of brittle solids. Attention to fatigue phenomena in alumina ceramics phenomenological to metals, having an endurance dependent on applied stress with a limit at around 50% of the single cycle fracture stress, was first drawn by the author in late sixties. Slip assisted fatigue process was not considered to be dominant in ceramic materials due to the absence of appreciable crack tip plasticity. With the background of this general survey of fatigue behaviour some fatigue studies based on mode of testing, theoretical and experimental analyses and fractographic evidence have been presented. Studies have shown that there is a dormant period between each successive crack advancement during which the residual stress and a plastic component is built up in a cumulative manner leading to eventual failure. During fatigue (plastic) and (residual stress) components are predominant for ductile metals and brittle glass/ceramics respectively. It is also apparent that dislocation assisted plastic component as a contributing factor in the failure of brittle materials under fatigue cannot be ruled out.     

Fatigue failure predictions for steels in the very high cycle region – A review and recommendations

Very high cycle fatigue properties of various steels were studied using findings of previous research and laboratory fatigue testing. First, experimental data for more than 550 specimens covering 25 high and medium strength steels were used to investigate the relationships between the applied stress, number of failure cycles, size of defects or inclusions at fracture origins and stress intensity factors. Using the results of the investigation of these data, general conclusions were arrived at for steels as a whole. It was observed that the size of the failure origin can be predicted using strength properties of steels. Existing methods for estimating major parameters such as size of failure origins and stress intensity factors were reviewed, new methods were proposed and their accuracy was verified using experimental data. Also, the possibility of simplifying existing formulae with substitutions for the major parameters was reviewed. Employing these major parameters, new formulae for predicting fatigue strengths of both medium and high strength steels were proposed. Predictions of these proposed formulae were compared with existing well known formulae using experimental data and statistical methods highlighting the simplicity and importance of the proposed formulae. The ability of employing the proposed formulae for predicting, “fatigue strengths that are more close to the real values” as well as “fatigue strengths that are more safe and conservative” was reviewed. Secondly, fatigue properties and failure causes of medium strength – low carbon structural steels that are usually used in civil engineering structures were investigated. For this investigation, 35 smooth specimens of five steels were tested using a rotating bending fatigue tester. It was observed that fatigue failures occur up to around 10⁷ cycles and that the failure originates from the surface. It was found that the formulae proposed are able to predict failures of these medium strengths steels. Slopes of stress life curves in the very high cycle fatigue regions were well predicted by these proposed formulae while the predictions were fairly aligned with values suggested in previous research. Finally, recommendations were given for employing suitable prediction methods considering safety and importance of components and structures.     

Grain Boundary Sliding in Fatigue of Pure Aluminum

The distributions of plastic strain near grain boundaries induced by fatigue loading were investigatedby the fiducial grid method in pure aluminum specimens, and the resulted grain boundary sliding(GBS) was systematically analysed. The results show that the strain field near a grain boundary isnonuniform. GBS is restricted by the junction of grain boundaries and causes discontinuities of bothdisplacement and strain. A peak value of shear strain was created in short-range area across the grainboundary. GBS plays an important role in cyclic softening and secondary hardening. The control fac-tor of GBS is the relative orientation between two grains and the macro orientation of the grainboundary rather than the ∑ value of the boundary.     

Role of Pits in Corrosion Fatigue of Offshore Structural Steel

From the corrosion fatigue test under intermit-tent wetting condition for offshore structural steelof A537 cl.l and data analysis,some results associ-ated with the role of pits in fatigue process havebeen discussed.     

Fatigue crack propagation in nickel-base superalloys – effects of microstructure,load ratio,and temperature

Abstract

The current state of knowledge and understanding of the long fatigue crack propagation behaviour of nickel-base superalloys are reviewed, with particular emphasis on turbine disc materials. The data are presented in the form of crack growth rate da/dN versus stress intensity factor range δK curves, and the effects of such variables as microstructure, load ratio R, and temperature in the near-threshold and Paris regimes of the curves, are discussed.

MST/521     

Hydrogen occlusivity and embrittlement in iron – effect of grain structure and cold work

Abstract

Experiments have shown that the amount of hydrogen occluded in iron for a given charging condition depends on both the ferritic grain size and the nature of the grain boundaries. The larger the relative misorientation between grains, the higher the occlusivity per unit grain-boundary area. With increasing grain size of the same grain–boundary nature, the boundaries are saturated more quickly, and thus the susceptibility to hydrogen damage is higher. In general, cold working increases the hydrogen uptake by increasing the defect density. When stressed parallel to the deformation axis, specimens cold worked to 20% deformation were shown to have a reduced ductility loss after hydrogen charging, thought to be a result of the development of texture.

MST/143     

A Method of Observing Fatigue Crack Growth by SEM

This paper introduces a modified control cir-cuit of static tensile stage of Cambridge S-200SEM.The function of the stage is extended to thatof a tensile/compressive dynamic fatigue testingstage.It can be used for studying fatigue microcharacteristic and crack growth.Direct observa-tions of small crack growth behaviour were carriedout under the SEM with modified stage.Resultsshowed the various stages in the development of acrack.     

Change in the philosophy of work†

Production contributes to the increase of ordered complexity. Quantitative growth in energy or other resource consumption may, beyond certain thresholds, be unimportant, if not destructive to ‘production’ in that sense. In certain cases, an equivalence can be stated between production and negative consumption. High efficiency in the use of energy and environmental resources is becoming an indicator of technological progress. High productivity leads to the need for redistributing work. Leisure work becomes more indicative of personalities than stupid professional work. Individual combinations of work elements (both paid and unpaid) rather than standardized professions will characterize people in the future.     

Relationship of Fatigue Crack Propagation to Dislocation Structure and Slip Geometry

The mechanisms of fatigue crack propagation are breifly reviewed in relation to Professor McClintock's contributions to the early development of the field. The most securely established understanding has been obtained for those mechanisms of propagation involving plasticity-inducedgeometrical changes to the crack tip during tensile and compressive straining (the plastic blunting process). The roles of more complex factors in controlling the kinetics of crack propagation,which cause the magnitude of the Paris exponent to exceed 2, remain to be elucidated. Recentlyobtained results revealing the interconnection between the slip behaviour at the crack tip, theplastic blunting process and the dislocation structures present in the material before the crackencounters them are reported.     

Understanding maintenance work in safety-critical organisations – managing the performance variability

Human and organisational performance variability has been identified as a cause of many latent and active failures in maintenance. Seldom has the variability been considered as an integral and inherent part of the maintenance activity to be managed by organisational means. The article deals with the challenge of understanding maintenance work in safety-critical organisations. The aim is to review the current literature on maintenance work and illustrate the organisational research challenges of managing performance variability in maintenance. This article presents six major research challenges in managing performance variability in maintenance. The article concludes by noting that a holistic theory on maintenance work is needed to manage the variability and turn it into a positive force. Maintenance has the potential to produce positive performance variability and guard against negative instability in complex sociotechnical systems.     

Non-saturated ion diffusion in concrete – A new approach to evaluate conductivity measurements

Non-saturated ion diffusion properties of cementitious materials were evaluated in an experimental study. To assess these properties, resistivity measurements have been performed on mortars with different binders (ordinary Portland cement – OPC, OPC with 5% silica fume, 40% slag and 70% slag, respectively) and different water-to-binder ratios (w/b, 0.38 and 0.53). Specimens have been conditioned to eight different climates with relative humidity (RH) from 100% to 33% RH in order to assess an effective diffusion coefficient. The results from the resistivity measurements have been corrected for changes of the conductivity of the pore solution when drying to different degrees of saturation.The diffusion coefficients for Portland cement binders within the range 100–59% RH are presented. They showed that the diffusion coefficient of the mortar with high w/b ratio was higher at high RH, but at low RH the opposite trend was found. By comparing these results with the corresponding desorption isotherms, it is shown that the diffusion coefficient for the two w/b ratios have the same dependency on the degree of saturation.     

Application of electrical capacitance tomography in particulate process measurement – A review

Particulate process measurement presents challenges because it often involves multiphase flow. Due to its advantages over other tomography modalities, electrical capacitance tomography (ECT) is widely applied in monitoring and measuring particulate processes. This paper presents a review on the application of ECT in particulate process measurement, including the monitoring of flow regime and solids distribution, solids flow velocity measurement, and fluidized bed dryers. The electrostatic phenomenon and the effect of electrostatics on the performance of ECT systems are also addressed. Finally, the challenges to ECT for particulate process measurement are given.