Bends in the plane with variable curvature

Explicit formulae for planar variable curvature bends are constructed using Euler’s method of natural equations. The bend paths are expressed in terms of special functions. It is shown that the length of the different bend types varies linearly with increasing radius and that the curvature of variable curvature bends can be expressed as a multiple of the curvature of a circle

A simulation approach to analyse the impacts of battery swap stations for e-motorcycles in Africa

Electric motorcycles are being introduced in some African countries to combat the negative environmental impacts from the rapid growth in the use of traditional internal combustion engine motorcycle taxis. However, the electricity systems in many of these countries are strained, with generation and/or distribution capacity at their limits, leading to regular power outages that could impact the charging of these e-motorcycles. These fragile grids may be put under further strain by additional e-motorcycle charging. Commercial motorcycle taxi drivers may not be willing to wait for extended periods to charge during their shift. The use of battery swapping stations could mitigate these issues. However, modelling of their system impacts is required to fully understand their potential. This paper presents a hybrid model to simulate the key operational processes of battery swapping stations and their energy systems, allowing various configurations and scenarios to be investigated for the specific context of e-motorcycles in Africa. The configuration parameters include the numbers of batteries and charging slots, the charging power, and the addition of solar PV and static battery energy storage capacity. Power outages can be modelled for various scenarios. A test case of a battery swap station in Nairobi, Kenya, was used to showcase and validate the model. The results demonstrated how the various sub-models performed and interacted with each other, and clearly showed what impact the chosen BSS configuration would have on the grid

Kilometric radiation power flux dependence on area of discrete aurora

Kilometer wavelength radiation, measured from distant positions over the North Pole and over the Earth's equator, was compared to the area of discrete aurora imaged by several low-altitude spacecraft. Through correlative studies of auroral kilometric radiation (AKR) with about two thousand auroral images, a stereoscopic view of the average auroral acceleration region was obtained. A major result is that the total AKR power increases as the area of the discrete auroral oval increases. The implications are that the regions of parallel potentials or the auroral plasma cavities, in which AKR is generated, must possess the following attributes: (1) they are shallow in altitude and their radial position depends on wavelength, (2) they thread flux tubes of small cross section, (3) the generation mechanism in them reaches a saturation limit rapidly, and (4) their distribution over the discrete auroral oval is nearly uniform. The above statistical results are true for large samples collected over a long period of time (about six months). In the short term, AKR frequently exhibits temporal variations with scales as short as three minutes (the resolution of the averaged data used). These fluctuations are explainable by rapid quenchings as well as fast starts of the electron cyclotron maser mechanism. There were times when AKR was present at substantial power levels while optical emissions were below instrument thresholds. A recent theoretical result may account for this set of observations by predicting that suprathermal electrons, of energies as low as several hundred eV, can generate second harmonic AKR. The indirect observations of second harmonic AKR require that these electrons have mirror points high above the atmosphere so as to minimize auroral light emissions. The results provide evidence supporting the electron cyclotron maser mechanism

Experimental investigation of bond behaviour of two common GFRP bar types in high-strength concrete

YesAlthough several research studies have been conducted on investigating the bond stress – slip behaviour of Glass-Fibre Reinforced Polymer (GFRP) bars embedded in high strength concrete (HSC) using a pull-out method, there is no published work on the bond behaviour of GFRP bars embedded in high strength concrete using a hinged beam. This paper presents the experimental work consisted of testing 28 hinged beams prepared according to RILEM specifications. The investigation of bond performance of GFRP bars in HSC was carried out by analysing the effect of the following parameters: bar diameter (9.5, 12.7 and 15.9 mm), embedment length (5 and 10 times bar diameter), surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) and bar location (top and bottom). Four hinged beams reinforced with 16 mm steel bar were also tested for comparison purposes. The majority of beam specimens failed by pull-out. Visual inspection of the test specimens showed that the bond failure of GFRP (HW-SC) bars usually occurred owing to the bar surface damage, while the bond failure of GFRP (SC) bars was caused due to the detachment of sand coating. The GFRP bars with helical wrapping and sand coated surface configurations showed different bond behaviour and it was found that the bond performance of the sand coated surface was better than that of the helically wrapped surface. Bond strength reduced as the embedment length and bar diameter increased. It was also observed that the bond strength for the bottom bars was higher than that of the top bars. The bond strength was compared against the prediction methods given in ACI-440.1R, CSA-S806 and CSA-S6 codes. All design guidelines underestimated the bond strength of both GFRP re-bars embedded in high strength concrete.Ministry of Higher Education in Libya for funding

Marxism and science studies: a sweep through the decades

This paper outlines the distinctive contribution of marxism to science studies. It traces the trajectory of marxist ideas through the decades from the origins of marxism to the present conjuncture. It looks at certain key episodes, such as the arrival of a Soviet delegation at the International History of Science Congress in London in 1931 as well as subsequent interactions between marxists and exponents of other positions at later international congresses. It focuses on the impact of several generations of marxists who have engaged with science in different ways. It examines the influence of marxism on contemporary trends in science studies. It concludes that marxism survives in circuitous and complex ways. It argues not only for a positive interpretation of its contribution in the past but for its explanatory and ethical power in the present and future

Adjustable levels of strong turbulence in a positive/negative ion plasma

Positive/negative ion plasmas, composed of Ba+, SF6−, and residual electrons, were observed to display characteristics of strong turbulence.Experiments on the UCI Q machine linked the presence of negative ions (and the depletion of electrons) with large density fluctuations (δn/n≂1), large‐amplitude, low‐frequency electrostatic noise (f≤20 kHz), and rapid transport of ions across magnetic field lines (D⊥≂104 cm2/sec). Ion velocity distributions were heated parallel to and cooled perpendicular to the confining magnetic field. The partial pressure of gaseous SF6 was shown to serve as a regulator of plasma turbulence. Turbulence levels could be smoothly varied from quiescent states (δn/n≂0.01) to strongly turbulent states (δn/n≂1)

ON THE PERSISTENCE OF SMALL REGIONS OF VORTICITY IN THE PROTOPLANETARY NEBULA

The fate of small regions of vorticity in a barotropic model of the protoplanetary nebula is investigated over thousands of years using a finite difference model. It is found that the coherence time for a small island of vorticity depends on its size, strength, orientation, and radial location in the nebula. Anticyclonic vorticity retains its coherence for longer times than cyclonic vorticity due to favorable interactions with the Keplerian shear flow. Rossby waves are generated as a result of mean vorticity gradients across the disk. The two-dimensional nebula evolves from discrete vortices into an axisymmetric flow consisting of small-amplitude vortex sheets at the radial locations of the initial vorticity. These vortex sheets induce an additional small, potential flow velocity superimposed on the Keplerian rotation curve

Using video in childbirth research: Ethical approval challenges

© The Author(s) 2015. Background: Conducting video-research in birth settings raises challenges for ethics review boards to view birthing women and research-midwives as capable, autonomous decision-makers. Aim: This study aimed to gain an understanding of how the ethical approval process was experienced and to chronicle the perceived risks and benefits. Research design: The Birth Unit Design project was a 2012 Australian ethnographic study that used video recording to investigate the physical design features in the hospital birthing space that might influence both verbal and non-verbal communication and the experiences of childbearing women, midwives and supporters. Participants and research context: Six women, 11 midwives and 11 childbirth supporters were filmed during the women’s labours in hospital birth units and interviewed 6 weeks later. Ethical considerations: The study was approved by an Australian Health Research Ethics Committee after a protracted process of negotiation. Findings: The ethics committee was influenced by a traditional view of research as based on scientific experiments resulting in a poor understanding of video-ethnographic research, a paradigmatic view of the politics and practicalities of modern childbirth processes, a desire to protect institutions from litigation, and what we perceived as a paternalistic approach towards protecting participants, one that was at odds with our aim to facilitate situations in which women could make flexible, autonomous decisions about how they might engage with the research process. Discussion: The perceived need for protection was overly burdensome and against the wishes of the participants themselves; ultimately, this limited the capacity of the study to improve care for women and babies. Conclusion: Recommendations are offered for those involved in ethical approval processes for qualitative research in childbirth settings. The complexity of issues within childbirth settings, as in most modern healthcare settings, should be analysed using a variety of research approaches, beyond efficacy-style randomised controlled trials, to expand and improve practice-based results