Gender differences in scientific productivity: a persisting phenomenon?

There is substantial literature on research performance differences between male and female researchers, and its explanation. Using publication records of 852 social scientists, we show that performance differences indeed exist. However, our case study suggests that in the younger generation of researchers these have disappeared. If performance differences exist at all in our case, young female researchers outperform young male researchers. The trend in developed societies, that women increasingly outperform men in all levels of education, is also becoming effective in the science system.     

Cavitation flow instability of subcooled liquid nitrogen in converging–diverging nozzles

The cavitation flow instability of subcooled liquid nitrogen in two types of converging–diverging (C–D) circular nozzles with throat diameters of 1.5 and 2.0 mm was experimentally investigated. Flow observations were also performed to clarify the instability phenomenon and the differences in cavitation behavior between the two nozzles. The cavitation mode changed from continuous mode to intermittent mode as the temperature of the subcooled liquid nitrogen decreased. This change occurred in both C–D nozzles when the temperature of the liquid reached approximately 76 K. Occurrence of the intermittent mode accompanying very large pressure-oscillations was considered to be caused by a drastic reduction of the speed of sound in the single-component, vapor–liquid flow because the speed of sound restricted the throat velocity in the C–D nozzle during cavitation. Oscillation pressure values in intermittent mode were much larger than those in continuous mode, peaking between 74 and 76 K. The magnitude of the oscillation pressure in intermittent mode could be evaluated from the difference between the throat static-pressure immediately prior to the occurrence of cavitation and that during cavitation.     

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.     

Investigations of fracture instability in crack growth for several metals—Part II: An energy approach for fracture instability analysis of crack growth

An energy approach is presented to predict fracture instability using elastic-plastic internal energy in structures, the physical behaviour of crack growth, dynamic effects in the process of unstable crack growth and intense strain region near the crack tip are considered. The practical forms of the approach have predicted correctly fracture instability of tests with three-point bending specimens (3PB specimen) and compact specimens (CT specimen) under highly stiff supporting system, but tearing modulus criterion gave incorrect estimations which were shown in part I [1].     

Thermal instability in freshwater lakes under ice: Effect of salt gradients or solar radiation?

The phenomenon of “temperature dichotomy”, or anomalous heating of surface water under the ice up to temperatures exceeding 4 °C is known to take place occasionally in solar-heated ice-covered freshwater lakes and has usually been explained by the stabilizing effect of the weak vertical salinity gradient created by the melt water flux from the ice and supporting the unstable temperature distribution. Here, we report an observation of the local temperature maximum in the upper part of the water column of ice-covered Lake Vendyurskoe (northwestern Russia). The observation was accompanied by vertically resolved measurements of the conductivity allowing estimation of the dissolved salts effect on the vertical density distribution. The results demonstrate insufficiency of the salt gradient to support the vertical stability of water column. Therefore, we suggest the vertically inhomogeneous radiation absorption to be the probable stabilizing mechanism here, similarly to radiatively heated boundary layers in the ocean, the atmosphere and star interiors. An analytical solution of the heat transfer equation is derived describing the temperature profile evolution in ice-covered lakes subject to solar radiation heating above the maximum density temperature. Observed daytime temperature profiles agree well with the analytical model that suggests the absence of convective mixing. According to the model, the temperature maximum is formed within a day that supports the hypothesis about the stabilizing effect of the solar radiation absorption. We conclude that in temperate lakes the warm layer should have diurnal character and should be destroyed during the nighttime by convection. In polar lakes, in turn, the warm layer can exist during essentially longer periods that is supported by application of the model to the previously published data from Lake Peters, Alaska. In this case, the ice melting rate can be significantly affected by the increased temperature gradient beneath the ice. Apart from potential effects on the ice melting rate and the spring plankton development in lakes, the regime represents a rare geophysical example of instability driven solely by radiative heating with many useful analogies in planetary and stellar physics.     

Dynamics of an elastic multibody chain: part a—body motion equations

In this paper—the first of a series describing the dynamics of an arbitrary multibody system—motion equations governing a set of individual bodies in a chain configuration are discussed. A chain consisting entirely of rigid bodies is considered first. Motion equations for a typical body of arbitrary shape and arbitrary mass distribution are then briefly summarized. Finally, the geometrical constraints necessary to connect the individual bodies into a chain are derived.

Large translational and rotational motions are permitted at the joints connecting contiguous bodies. In other words, both prismatic and revolute joints are included, alone and in combination. As well, the interbody force constraints required to ensure that equal but opposite forces and torques exist at each joint are developed. The resulting expressions are amenable to the introduction of constraint and control forces at the chain joints. This permits the number of actively controlled degrees of freedom at any specific joint to be arbitrarily specified. The equations are fully nonlinear in the ‘rigid’ velocities for all individual chain bodies.

The analysis is then extended to the case of a chain consisting of an arbitrary number of elastic bodies. Each elastic body is assumed to possess an arbitrary stiffness distribution, although structural deformations are assumed to be small.     

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.     

Differential charging in X-ray photoelectron spectroscopy: a nuisance or a useful tool?

We apply a negative bias to the sample while recording an XPS spectrum to enhance differential (positive) charging. The enhanced differential charging is due to the repulsion of stray electrons from the sample, which normally cause partial neutralization of the poorly conducting samples or regions accumulating positive charging, as a consequence of the photoelectron emission. This enhanced differential charging (obtained by negative biasing) is shown to have the ability to separate otherwise overlapping peaks of PDMS layer from that of the SiO(2)/Si substrate. Each layer experiences different charging that can be used to derive information related to dielectric properties of the layers, proximity of the atoms within composite multilayers, or both. Hence, differential charging in XPS, which is usually considered as a nuisance, is turned into a useful tool for extracting additional information from nanometer-size surface structures.     

Retired engineers: a growing liability or a resource?

In the Western world, the number of people in retirement is growing at an unprecedented rate. There is a lot of potential among the elderly, especially among retired engineers, which ought to be harnessed and encouraged for the benefit of the nation and also for the individuals themselves. The article explores this situation and suggests some ways of tapping this resource     

The Lithium/Air Battery: Still an Emerging System or a Practical Reality?

Lithium/air is a fascinating energy storage system. The effective exploitation of air as a battery electrode has been the long‐time dream of the battery community. Air is, in principle, a no‐cost material characterized by a very high specific capacity value. In the particular case of the lithium/air system, energy levels approaching that of gasoline have been postulated. It is then not surprising that, in the course of the last decade, great attention has been devoted to this battery by various top academic and industrial laboratories worldwide. This intense investigation, however, has soon highlighted a series of issues that prevent a rapid development of the Li/air electrochemical system. Although several breakthroughs have been achieved recently, the question on whether this battery will have an effective economic and societal impact remains. In this review, a critical evaluation of the progress achieved so far is made, together with an attempt to propose future R&D trends. A forecast on whether Li/air may have a role in the next years' battery technology is also postulated.     

Cavitation in Liquid Helium Observed in a Flow Due to a Vibrating Quartz Fork

A quartz fork vibrating at high amplitude is used to study cavitation in He I and He II along the saturated vapor pressure (SVP) curve and at slightly elevated pressures. Cavitation is observed as a breakdown of the resonance response at critical velocity when slowly sweeping the frequency of the drive across the resonance and confirmed by visual observation of a bubble occurring in He II in the space between the prongs of the fork. On decreasing the temperature from 4.2 K along the SVP curve the critical velocity slowly increases from about 0.4 m/s to 1 m/s, until a steep increase up to about 2 m/s occurs within about 20 mK just below the superfluid transition. We discuss our results, including the measured dependence of the critical velocity versus overpressure at fixed bath temperature.      

Minimum cement content requirements: a must or a myth?

The objective of the present work was to systematically investigate the issue of minimum cement content requirements, by studying the behavior of concretes with different water to cement ratios ( w/c) in the range of 0.45–0.70, in which the cement content was varied, by controlling the water content, using water reducing admixtures. The effect of cement content was noted to be different for various properties: strength was a function of w/c and independent of cement content; total water absorption was proportional to the paste content at a given w/c, while capillary absorption and chloride ingress reduced with a reduction in the cement content for a given w/c, to an extent which was much greater than the reduction in total porosity. Carbonation and shrinkage were largely independent of cement content for a given w/c. The trends observed were discussed in terms of the effect of paste content on concrete properties, and the influence of admixtures on the paste properties. These results suggest that requirements for minimum cement content in standards should be revisited.     

Is an oscillator-based measurement adequate in a liquid environment?

Oscillator-based measurements with quartz crystal resonators are analyzed. The investigations have shown that classical thickness monitors as well as many chemical vapor sensors based on a quartz crystal microbalance (QCM) work properly, even with simple oscillators. It was demonstrated that, for applications in a liquid environment, more sophisticated electronics are necessary. Also a comparison between the experimental results in liquids and the theoretical predictions is hardly possible without the knowledge of the oscillator behavior. As our solution, we present an automatic gain-controlled oscillator with two output signals, the oscillator frequency, and a signal that represents the damping of the quartz resonator. A calibration method is introduced, which allows one to calculate the series resonance frequency f/sub s/ and the series resistance R/sub s/ from these oscillator signals.     

Characteristic crack-tip distances in fracture criteria: Is crack propagation discontinuous?

The present paper describes a possible mechanism for discontinuous crack advance in which surface separation occurs initially not at the crack-tip itself but within the crack-tip plastic zone of size r_p, at the mid-point of the crack-tip characteristic distance d (identified here with the finite growth step Δa), i.e., at the region of maximum opening tensile stress, spreading towards (and also away from) the crack-tip. The crack extension occurs when the crack-tip is reached and full opening over the distance d is completed.Finite element analyses show that this mechanism causes the formation of a rippled crack face surface in elastic-plastic materials in which irreversible plastic deformations take place during each growth step, in sharp contrast with the smooth surface created in ideal elastic materials in which all deformations are fully reversible. Some pictorial evidence of void formation ahead of the crack tip and of ripples during propagation, found in the literature, is presented.Although the present analysis is from a continuum standpoint it is acknowledged that micro structural features and mechanisms can condition the fracture events taking place in the process zone.The implication to the brittle-ductile transition of the dependence of the energy release rate, G^ΔΞ, on the ratio q (=Δa/r_p) is also discussed.     

Managing flexible manufacturing technology: Must parts in an FMS always move in a job-shop manner?

The literature typically assumes that an FMS consists of a number of machines of different processing capability. Furthermore, in view of the inherent flexibility of an FMS, many researchers believe that 'flexible' implies that a wide variety of parts can be, and should be, processed simultaneously in an FMS. To do otherwise will inevitably mean some machines are idle and hence the FMS may become a tremendous waste. This paper is an attempt to study this issue. Unlike a job shop, which is typically an eclectic collection of machines of different process capabilities, most flexible manufacturing systems consist of only one or two types of versatile programmable machines. We contend that the FMS machines are analogous to the multi-skilled workers in lean production. In lean production, workers work in teams. It is common for each team to work on one job at a time, from start to finish. Jobs are not passed around from worker to worker. Likewise, machines in an FMS can be assigned into 'teams', where each 'team' is dedicated to process a single part type (or family) at a time. Parts do not necessarily have to move from machine to machine in a job shop manner.     

On elastic–plastic fracture behavior of a bi-layered composite plate with a sub-interface crack under mixed mode loading

A generalized Irwin model is proposed to investigate elastic–plastic fracture behavior of a bi-layered composite plate with a sub-interface crack under combined tension and shear loading. The dependence of the stress intensity factors, the plastic zone size, the effective stress intensity factor and the crack tip opening displacement on the crack depth h, the Dundurs’ parameters and the phase angle θ is discussed in detail. Numerical results show that in most cases, if the crack is embedded in a stiffer material, when the crack is close to the interface, the plastic zone size and the crack tip opening displacement will increase. On the contrary, if the crack is embedded in a softer material, when the crack is close to the interface, the plastic zone size and the crack tip opening displacement will decrease.     

Mechanical analysis of fracture in an automotive radiator head produced from a nylon–glass fibre composite

The fracture during assembly of a radiator head produced from a nylon–short glass fibre composite is studied in the framework of complexities such as determining elastic constants and fracture stresses on the one hand and manufacturing problems such as distortion after moulding and deformations induced during assembly on the other. The combination of in situ measurements, SEM observation of fracture surfaces and reverse modelling of non-linear material properties permitted to make a sufficiently accurate estimate of the real mechanical behaviour of the material, as opposed to the properties mentioned in its data sheet. While the method was applied to solve a particular production problem, its applicability in process evaluation and redesign of injection-moulded short fibre composites is general.     

Caffeine in your drink: natural or synthetic?

Owing to possible adulteration and health concerns, it is important to discriminate between natural and synthetic food ingredients. A new method for compound-specific isotope analysis (CSIA) by coupling high-temperature reversed-phase liquid chromatography to isotope ratio mass spectrometry (HT-RPLC/IRMS) was developed for discrimination of natural and synthetic caffeine contained in all types of drinks. The analytical parameters such as stationary phase, column inner diameter, and column temperature were optimized for the separation of caffeine directly from drinks (without extraction). On the basis of the carbon isotope analysis of 42 natural caffeine samples including coffee beans, tea leaves, guaraná powder, and maté leaves, and 20 synthetic caffeine samples from different sources by high-temperature reversed-phase liquid chromatography coupled to isotope ratio mass spectrometry, it is concluded that there are two distinguishable groups of caffeine δ(13)C-values: one between -25 and -32‰ for natural caffeine, and the other between -33 and -38‰ for synthetic caffeine. Isotope analysis by HT-RPLC/IRMS has been applied to identify the caffeine source in 38 drinks. Four mislabeled products were detected due to added but nonlabeled synthetic caffeine with δ(13)C-values lower than -33‰. This work is the first application of HT-RPLC/IRMS to real-world food samples, which showed several advantages: simple sample preparation (only dilution), high throughput, long-term column stability, and high precision of δ(13)C-value. Thus, HT-RPLC/IRMS can be a very promising tool in stable isotope analysis of nonvolatile compounds.