Local Technological and Demographic Effects on Electricity Transmission: A Spatially Lagged Local Estimation of New England Marginal Losses

Electricity transmission is subject to distribution losses and congestion costs. Economists have prior theorized that these transmission imperfections could create divided markets with electricity generating spatial oligopolists. This concern has been largely dismissed because of recent technological advances in electricity transmission. The effects of local technological and demographic indicators on electricity transmission costs remains both commonly accepted as negligible and spatially untested. This analysis employs a spatially lagged local estimation of New England’s marginal electricity losses with respect to both technological and demographic indicators. The results of this analysis are consistent with the widely accepted notion that technological advances have mitigated the effect of local distribution losses and local congestion costs on electricity prices

Les reseaux hvdc multi-terminaux: des defies multipes en genie electrique high voltage direct current grid multiterminals: many challenges in electrical engineering

Electrical installation using high voltage need to be improve to make the exchanges of power under the sea with security and to connect the offshore sources. Alterative grid show limits in those applications. High voltage direct current (HVDC) installation can be a solution to those cases, if some technological and scientist problem are solved. Challenge are in every level of the electrical engineering work, in the whole system, with the material used, and the way their used. This article introduce the main challenges in the domain of electrical engineering to solve in case of the exploitation of a HVDC grid

The unidirectional relationship of nightmares on self-harmful thoughts and behaviors

Understanding the direction of the predictive relationship between nightmares and suicidal behaviors is important to model its underlying mechanisms. We examine the direction of this relationship and the mediating role of negative affect. A fixed interval diary study obtained pre-sleep and post-sleep measures of affect, nightmares, and self-harmful thoughts and behaviors (SHTBs) from 72 university students (88.9% female). The results show predictive utility of nightmares on SHTBs - indicating a fourfold increased risk of SHTBs. Additionally, results support the suggestion of a unidirectional predictive influence (of nightmares on likelihood of SHTBs but not vice versa). Moreover, postsleep negative affect partially mediated the relationship between nightmares and postsleep SHTBs. This empirically validates assumptions of directionality for future models

How do we know educational interventions work?

© 2024 Kevin D. Hochard. This AAM is provided for your own personal use only. It may not be used for resale, reprinting, systematic distribution, emailing, or for any other commercial purpose without the permission of the publisher.The overall aim of this chapter is to focus on the process of, and issues warranting consideration for, the evaluation of educational interventions. In particular, to outline some key considerations for educators to follow when assessing the evidence-base for interventions they might be considering for use in their practice. Also, important considerations for those wishing to evaluate the effectiveness of an intervention they have initiated, as well as a useful checklist which summarises this all. Recognising that some readers of this chapter might be practitioners rather than researchers, it has been written with the practitioner in mind in, hopefully, a simple and practical way. There are, however, further opportunities for additional reading and resources signposted throughout for those who wish to read up on any of these areas more. In addition to those cited throughout and referenced in the Reference list at the end, there is also section that provides the author’s Additional recommended Readings and Resources to follow-up on. Readers might also want to refer to Chapter 3 in this book which discusses Single versus Multiple PPI approaches

Dynamic instability of supercritical driveshafts mounted on dissipative supports ― effect of viscous and hysteretic internal damping

International audienceThe case of a rotating shaft with internal damping mounted either on elastic dissipative bearings or on infinitely rigid bearings with viscoelastic suspensions is investigated in order to obtain the stability region. A Euler–Bernoulli shaft model is adopted, in which the transverse shear effects are neglected and the effects of translational and rotatory inertia, gyroscopic moments, and internal viscous or hysteretic damping are taken into account. The hysteretic damping is incorporated with an equivalent viscous damping coefficient. Free motion analysis yields critical speeds and threshold speeds for each damping model in analytical form. In the case of elastic dissipative bearings, the present results are compared with the results of previous studies on finite element models. In the case of infinitely rigid bearings with viscoelastic suspensions, it is established that viscoelastic supports increase the stability of long shafts, thus compensating for the loss of efficiency which occurs with classical bearings. The instability criteria also show that the effect of the coupling which occured between rigid modes introducing external damping and shaft modes are almost more important than damping factor. Lastly, comparisons between viscous and hysteretic damping conditions lead to the conclusion that an appropriate material damping model is essential to be able to assess these instabilities

On the tension-tension fatigue behaviour of a carbon reinforced thermoplastic part II: evaluation of a dumbbell-shaped specimen

International audienceFor performing uni-axial fatigue tests on composite materials, ASTM D3479/D3479M Standard Test Method for Tension–Tension Fatigue of Polymer Matrix Composite Materials is often considered. This standard prescribes a rectangular shaped specimen with end tabs. However, in part I of this study it became clear that for some materials, such as the carbon PPS under study, the proposed geometry is not ideal for fatigue tests. In this manuscript, a dumbbell (dogbone) shape is assessed to see whether it performs better under fatigue loading conditions, primarily meaning that failure does not occur in the tabbed section. The shape is first optimised using finite element modelling, after which fatigue experiments are performed. It may be concluded, for the material under study, that the dumbbell shape is preferable to rectangular since failure never occurred under or near the tabbed section, and fatigue life is highly underestimated when using the rectangular specimen

Dynamics of a supercritical composite shaft mounted on viscoelastic supports

International audienceThe damping in a carbon fiber reinforced plastic (CFRP) laminate is greater than that which occurs in most metallic materials. In the supercritical regime, the damping can trigger unstable whirl oscillations, which can have catastrophic effects. The vibrations occurring in a supercritical composite drive shaft are investigated here in order to predict instabilities of this kind. A simply supported carbon/epoxy composite tube mounted on viscoelastic supports is studied, using an approximation of the Rayleigh-Timoshenko equation. The damping process is assumed to be hysteretic. The composite behavior is described in terms of modulus and loss factor, taking homogenized values. The critical speeds are obtained in several analytical forms in order to determine the effects of factors such as the rotatory inertia, the gyroscopic forces, the transverse shear and the supports stiffness. Assuming that the hysteretic damping can be expressed in terms of the equivalent viscous model, the threshold speed is obtained in the form of an analytical criterion. The influence of the various factors involved is quantified at the first critical speed of a subcritical composite shaft previously described in the literature. The influence of the coupling mechanisms on the unsymmetrical composite laminate and the end fittings is also investigated using a finite element model. None of these parameters were found to have a decisive influence in this case. Those having the greatest effects were the transverse shear and the supports stiffness. The effects of the composite stacking sequence, the shaft length and the supports stiffness on the threshold speed were then investigated. In particular, drive shafts consisting only of ±45° or ±30° plies can be said to be generally unstable in the supercritical regime due to their very high loss factors

Design of high rotation frequency composite tubes

International audienceThis work relates to the sizing of subcritical and supercritical laminated composite drive shafts. The hollows drive shafts are designed to transmit the torsional load and to minimize the dynamic effects due to rotation. To meet this need, these structures must combined strength, rigidity and lightness. New high modulus carbon fibres can be adapted to a progress in this field. This work presents sizing tools for optimisation of supercritical drive shafts mounted on viscoelastic suspensions. Two items are discussed: dynamic analysis (response to forces excitation; free motion; instability), strength (buckling of thin tubes; torsional strength). Supercritical drive shafts examples made of high modulus fibres or high-strength fibres are presented

Optimisation of hybrid high-modulus/high-strength carbon fibre reinforced plastic composite drive shafts

International audienceThis study deals with the optimisation of hybrid composite drive shafts operating at subcritical or supercritical speeds, using a genetic algorithm. A formulation for the flexural vibrations of a composite drive shaft mounted on viscoelastic supports including shear effects is developed. In particular, an analytic stability criterion is developed to ensure the integrity of the system in the supercritical regime. Then it is shown that the torsional strength can be computed with the maximum stress criterion. A shell method is developed for computing drive shaft torsional buckling. The optimisation of a helicopter tail rotor driveline is then performed. In particular, original hybrid shafts consisting of high-modulus and high-strength carbon fibre reinforced epoxy plies were studied. The solutions obtained using the method presented here made it possible to greatly decrease the number of shafts and the weight of the driveline under subcritical conditions, and even more under supercritical conditions. This study yielded some general rules for designing an optimum composite shaft without any need for optimisation algorithms