Suspension biomechanics of swimming microbes

Micro-organisms play a vital role in many biological, medical and engineering phenomena. Some recent research efforts have demonstrated the importance of biomechanics in understanding certain aspects of micro-organism behaviours such as locomotion and collective motions of cells. In particular, spatio-temporal coherent structures found in a bacterial suspension have been the focus of many research studies over the last few years. Recent studies have shown that macroscopic properties of a suspension, such as rheology and diffusion, are strongly affected by meso-scale flow structures generated by swimming microbes. Since the meso-scale flow structures are strongly affected by the interactions between microbes, a bottom-up strategy, i.e. from a cellular level to a continuum suspension level, represents the natural approach to the study of a suspension of swimming microbes. In this paper, we first provide a summary of existing biomechanical research on interactions between a pair of swimming micro-organisms, as a two-body interaction is the simplest many-body interaction. We show that interactions between two nearby swimming micro-organisms are described well by existing mathematical models. Then, collective motions formed by a group of swimming micro-organisms are discussed. We show that some collective motions of micro-organisms, such as coherent structures of bacterial suspensions, are satisfactorily explained by fluid dynamics. Lastly, we discuss how macroscopic suspension properties are changed by the microscopic characteristics of the cell suspension. The fundamental knowledge we present will be useful in obtaining a better understanding of the behaviour of micro-organisms.     

Testing the science/technology relationship by analysis of patent citations of scientific papers after decomposition of both science and technology

This study analyzes more than three decades of theory testing published in leading entrepreneurship journals. It uncovers the amount of theory testing; the extent to which theories are tested multiple times; and, the disciplinary origins of the theories that are tested. The analysis reveals that empirical researchers have increasingly responded to demands for more theory-driven knowledge over time through domestic theory creation and wholesale adoption of theories from other fields. It is observed that the most tested theories are borrowed from other scientific fields. The value of agency theory, the most popular one, is assessed via a foreign theory screening model. The result suggests that researchers cannot be too cautious when considering foreign theory for domestic knowledge development. Ultimately, researchers are strongly encouraged to consider testing the many domestic theories that have been specifically designed to answer the pressing, practical problems of the entrepreneurship discipline.     

Negative results are disappearing from most disciplines and countries

Concerns that the growing competition for funding and citations might distort science are frequently discussed, but have not been verified directly. Of the hypothesized problems, perhaps the most worrying is a worsening of positive-outcome bias. A system that disfavours negative results not only distorts the scientific literature directly, but might also discourage high-risk projects and pressure scientists to fabricate and falsify their data. This study analysed over 4,600 papers published in all disciplines between 1990 and 2007, measuring the frequency of papers that, having declared to have “tested” a hypothesis, reported a positive support for it. The overall frequency of positive supports has grown by over 22% between 1990 and 2007, with significant differences between disciplines and countries. The increase was stronger in the social and some biomedical disciplines. The United States had published, over the years, significantly fewer positive results than Asian countries (and particularly Japan) but more than European countries (and in particular the United Kingdom). Methodological artefacts cannot explain away these patterns, which support the hypotheses that research is becoming less pioneering and/or that the objectivity with which results are produced and published is decreasing.     

Atomistic study of vibrational properties of γ-Al2O3

A study of the vibrational density of states (DOS) of γ-Al₂O₃ is presented. Four structural models from the recent literature are considered: vacant spinel model and three nonspinel models. The vacant spinel and one of the nonspinel models have unit cells with 40 atoms, while the other two models have 160 atoms. The interatomic interactions are computed using classical force fields that include Coulomb and van der Waals attractive interactions, short range repulsive interactions, as well as three-body terms. The oxygen polarizability is included via a core-shell potential. The DOS is compared with ab initio calculations recently published for the vacant spinel model. The classical and ab initio DOS show some differences for frequencies higher than 200 cm⁻¹, the ab initio having more peaks and having a frequency cutoff 100 cm⁻¹ lower than the classical DOS. The DOS of all models present some small differences. While the 160-atoms nonspinel models present a rather structureless DOS, 40-atoms models present peaks and dips relative to the 160-atoms models. The elastic constants of polycrystalline γ-Al₂O₃ are also estimated using several force fields. In general, the classical force field predict higher elastic moduli than the ab initio method. The infrared spectra of the four models are calculated.     

Nanoscale research in South Africa: A mapping exercise based on scientometrics

This article reports the findings of a scientometric analysis of nanoscale research in South Africa during the period 2000–2005. The ISI databases were identified as the most appropriate information platform for the objectives of the investigation and have been interrogated for the identification of South African authors publishing in the field. The article identifies trends over time, major institutional contributors, journals in which South African authors publish their research, international collaborators and performance in comparison to four comparator countries (India, Brazil, South Korea and Australia). The major findings of the investigation are as follows: nanoscale research in South Africa is driven by individual researchers interests up to date and it is in its early stages of development; the country’s nanoscale research is below what would one expect in light of its overall publication output; the country’s nano-research is distributed to a number of Universities with subcritical concentration of researchers.     

Nonlinear instability in flagellar dynamics: a novel modulation mechanism in sperm migration?

Throughout biology, cells and organisms use flagella and cilia to propel fluid and achieve motility. The beating of these organelles, and the corresponding ability to sense, respond to and modulate this beat is central to many processes in health and disease. While the mechanics of flagellum–fluid interaction has been the subject of extensive mathematical studies, these models have been restricted to being geometrically linear or weakly nonlinear, despite the high curvatures observed physiologically. We study the effect of geometrical nonlinearity, focusing on the spermatozoon flagellum. For a wide range of physiologically relevant parameters, the nonlinear model predicts that flagellar compression by the internal forces initiates an effective buckling behaviour, leading to a symmetry-breaking bifurcation that causes profound and complicated changes in the waveform and swimming trajectory, as well as the breakdown of the linear theory. The emergent waveform also induces curved swimming in an otherwise symmetric system, with the swimming trajectory being sensitive to head shape—no signalling or asymmetric forces are required. We conclude that nonlinear models are essential in understanding the flagellar waveform in migratory human sperm; these models will also be invaluable in understanding motile flagella and cilia in other systems.     

Explicit analysis technique for nonlinear inverse mechanics problems

Nonlinear material models are conventionally used in forward analysis to predict the global mechanical response of boundary value problems. Such models are not expected to exactly reproduce global experimental response in all cases. Accordingly, the measured global response at specific domain or surface points can guide an inverse nonlinear structural analysis to successively recover a representative material model. By assuming an initial set of stress–strain data points, the load–displacement response at the control points is computed in a forward incremental analysis without iterations. This analysis retains the stresses at the integration points. The corresponding strains are not expected to be accurate since the computed displacements are not anticipated to match the measured displacements at the control points. Therefore, a conjugate incremental displacement analysis is performed at the same load steps to correct for displacements and strains everywhere by matching the measured displacements at the control points. It is found that the predicted stress–strain data set at the most highly stressed integration point provides the most accurate representation of an improved material model. This data set is used in the next two-phase incremental analysis pass as the material model. The process is repeated until the forward analysis phase reproduces the measured displacements at the control points requiring no corrections. Accordingly, the selection of a single stress–strain data set yields an explicit recovery of the nonlinear elasticity material model without any interpolation or averaging schemes, which significantly reduces data storage and computational effort. The applicability of the present explicit approach is demonstrated on simple mechanical models, a skeletal structural system and a 2D finite element mesh.     

Asymptotic analysis of the small-scale structure of the laminar boundary layer with suction

The features of the gas flow in the working section of a transonic wind tunnel have been considered. On the basis of the method of joining asymptotic expansions and the theory of detached zones mathematical models of the flow are proposed. The flow over a perforation and transverse and longitudinal slots has been investigated. In the latter case, a nonstationary and a stationary analogy with a two-dimensional flow are stated. A deflector — a new device for reflecting shocks — is proposed. The problems are discussed.     

Experimental investigation of the methods of energy supply to the external surface of models of flying vehicles

The results of investigation of the effects of external supply of energy to the wind tunnel models at the Mach number M=5 are presented. The energy supply has been modeled by a light gas (helium) supply to the models. The loads have been measured by wind-tunnel balance. It is obtained that at small angles of attack the lift increment under the external supply of energy occurs without an increase in drag and under some conditions is more efficient than the lift increase by means of higher engine thrust under the same energy supply to it. The similarity criterion (“influence coefficient”) is proposed to relate the wind tunnel results to full-scale conditions. Based on the fact that the application of hot hydrogen is the most reasonable for the external supply of energy under full-scale conditions, the aspects of accelerating its ignition and combustion at low temperatures are investigated. It is shown that addition into the hydrogen of its atoms and activated molecules by passing the hydrogen through a glow-discharge zone makes it possible to implement ignition at a temperature of ∼300 K. Without such a treatment, ignition occurs at a temperature of ∼900 K.     

References,authors, journals and scientific disciplines underlying the sustainable development literature: a citation analysis

This paper identifies the main references, authors and journals influencing the sustainable development literature. The task is accomplished by means of a citation analysis based on the records of ISI Web of Science. We found that the core of sustainability thinking is framed by a pattern of landmark studies published around every 5 years. Only 380 publications have been cited at least ten times. References with the highest influence are those with a global dimension and large diffusion, such as Brundtland Commission’s “Our common future” (1987) and classics such as Meadows’ et al. “Limits to growth” (1972). The list of the most influential references over the period 1960–2005 is dominated by contributions from economics (particularly ecological economics) and environmental science, but includes many other disciplines such as urban planning, political sciences and sociology. References are also made to policy documents such as “Agenda 21”, one of the main outcomes of the Rio Summit in 1992. In analyzing citation trends, we found that classics, because of their high rates of citations per year, seem to have a more enduring and stable influence.     

Horndal at Heathrow? Capacity creation through co-operation and system evolution

At Europe's most congested airports demand for take-off andlanding slots has exceeded the available supply for many years.Yet, in the face of persistent growth in air traffic activities,these airports have achieved remarkable increases in their capacitiesto handle flights, despite retaining the same basic infrastructures.This paper investigates this growth of capacity as a ‘problemcentred innovating system’, in which the roles of proceduralchange and co-operation between teams are highlighted. ‘Systemevolution’ is also observed, as over time new agents withdifferent knowledge bases have been brought into ‘thesystem’ to assist with the search for additional capacity.     

Modern computer assisted methods in metallurgy

Image analysis systems have been used in metallurgy for over two decades and play a vital role in quality assessment for the steel industry. One major application is the characterization of steel by counting and measuring the non-metallic inclusion content. Visual steel assessment, relying on the comparison with idealized ‘charts’ of varying inclusion content, for example as defined byastm andsep, is the most common manual method employed. However, this has proved to be most difficult to automate due to the degree of subjectivity associated with the manual methods. This has previously restricted the acceptance of image analysis systems for routine quality control. The increased software power of the more modern instruments has enabled the installation of systems which satisfactorily mimic the skilled observer in a reproducible manner. These work with an economically attractive throughput and produce results in the accepted standard format. A limitation of these systems is that they grade a field on the basis of the majority inclusion type present. This can lead to significant but lesser inclusions being ignored altogether and presenting a false picture of the sample. This paper describes a new method which separately identifies individual inclusions in a field. The grade number of a field can then be determined for each inclusion type. This is known as the mixed field method. This paper describes this method and its implementation on the Cambridge Instruments’quantimet 920 image analysis system.     

Amelogenin is phagocytized and induces changes in integrin configuration,gene expression and proliferation of cultured normal human dermal fibroblasts

Fibroblasts are central in wound healing by expressing important mediators and producing and remodelling extracellular matrix (ECM) components. This study aimed at elucidating possible mechanisms of action of the ECM protein amelogenin on normal human dermal fibroblasts (NHDF). Amelogenin at 100 and 1000 μg/ml increased binding of NHDF via several integrins, including αvβ3, αvβ5 and α5β1. Further, both surface interaction and cellular uptake of amelogenin by NHDF was observed using scanning and transmission electron microscopy. Gene microarray studies showed >8-fold up or down-regulation of genes, of which most are involved in cellular growth, migration and differentiation. The effect of amelogenin was exemplified by increased proliferation over 7 days. In conclusion, the beneficial effects of amelogenin on wound healing are possibly conducted by stimulating fibroblast signalling, proliferation and migration via integrin interactions. It is hypothesized that amelogenin stimulates wound healing by providing connective tissue cells with a temporary extracellular matrix.     

Thermoelastic Stress Analysis of a GRP Tee Joint

A detailed study of the stresses that are developed in a glass reinforced plastic (GRP) tee joint under service loads is described. The joints are fabricated by laminating a boundary angle over a radiused fillet on either side of the ‘tee’. Full-field stress characterisation data is provided by a thermoelastic analysis of the tee joint. Calibration procedures that allow the thermoelastic data to be compared with the results of a finite element analysis are detailed. The results of the thermoelastic analysis are compared with values obtained from the finite element analysis. The applicability of thermoelastic analysis as a validation tool for finite element models of composite materials is assessed.     

A partial least squares solution to the problem of multicollinearity when predicting the high temperature properties of 1Cr–1Mo–0.25V steel using parametric models

Recently there has been renewed interest in assessing the predictive accuracy of existing parametric models of creep properties, with the recently develop Wilshire methodology being largely responsible for this revival. Without exception, these studies have used multiple linear regression analysis (MLRA) to estimate the unknown parameters of the models, but such a technique is not suited to data sets where the predictor variables are all highly correlated (a situation termed multicollinearity). Unfortunately, because all existing long-term creep data sets incorporate accelerated tests, multicollinearity will be an issue (when temperature is held high, stress is always set low yielding a negative correlation). This article quantifies the severity of this potential problem in terms of its effect on predictive accuracy and suggests a neat solution to the problem in the form of partial least squares analysis (PLSA). When applied to 1Cr–1Mo–0.25V steel, it was found that when using MLRA nearly all the predictor variables in various parametric models appeared to be statistically insignificant despite these variables accounting for over 90% of the variation in log times to failure. More importantly, the same linear relationship appeared to exist between the first PLS component and the log time to failure in both short and long times to failure and this enabled more accurate extrapolations to be made of the time to failure, compared to when the models were estimated using MLRA.     

The effects of temperature on the molecular orientation of zinc phthalocyanine films

Phthalocyanine compounds have been widely investigated as candidate materials for technological applications, which is mainly due to their thermal stability and possibility of processing in the form of thin films. In most applications, the controlled growth of thin films with high crystalline quality is essential. In this study, zinc phthalocyanine (ZnPc) thin films were prepared by evaporation on glass and Au-coated glass substrates with subsequent annealing at different temperatures in ambient atmosphere. The morphological and structural features of 80 nm thick zinc phthalocyanine films were investigated, evidencing an α → β phase transformation after annealing the films at 200 °C, as indicated by UV–Vis spectroscopy and FTIR analyses. A better uniformity of the annealed films was also evidenced via AFM analysis, which may be of importance for applications where film homogeneity and excellent optical quality are required.     

Localised formulations for thick “sandwich” laminated and composite structures

A “sandwich” panel under axial compressive loading is studied over its post-buckling range. Alternative formulations were developed to cover solutions other than the deflection shape given by the classical Rayleigh-Ritz analysis. General elasticity principles are used to derive the total potential energy function in terms of the displacement field. Given a constant modal amplitude displacement field, which is introduced in the total potential energy function, the results are discussed having as background models studied earlier. Techniques for the analysis of localized solutions are presented with reference to the study of the beam on nonlinear elastic foundation. The concepts of localization are introduced by using dynamical analogy and the double scale perturbation method and applied to the sandwich panel, to derive the governing amplitude modulation equations. The resulting formulations are discussed using some examples, and by solving analytical and numerically the amplitude differential equations.     

Exploring the management information systems discipline: a scientometric study of ICIS, PACIS and ASAC

This paper examines the rapid growth of China in the field of nanotechnology and the rise of collaboration between China and the US in this emerging domain. Chinese scientific papers in nanotechnology are analyzed to indicate overall trends, leading fields and the most prolific institutions. Patterns of China–US nanotechnology paper co-authorship are examined over the period 1990–2009, with an analysis of how these patterns have changed over time. The paper combines bibliometric analysis and science mapping. We find rapid development in the number of China–US co-authored nanotechnology papers as well as structural changes in array of collaborative nanotechnology sub-fields. Implications for both China and the US of this evolving relationship are discussed.