A Topological Investigation of Phase Transitions of Cascading Failures in Power Grids

Cascading failures are one of the main reasons for blackouts in electric power transmission grids. The economic cost of such failures is in the order of tens of billion dollars annually. The loading level of power system is a key aspect to determine the amount of the damage caused by cascading failures. Existing studies show that the blackout size exhibits phase transitions as the loading level increases. This paper investigates the impact of the topology of a power grid on phase transitions in its robustness. Three spectral graph metrics are considered: spectral radius, effective graph resistance and algebraic connectivity. Experimental results from a model of cascading failures in power grids on the IEEE power systems demonstrate the applicability of these metrics to design/optimize a power grid topology for an enhanced phase transition behavior of the system

Center of mass velocity-based predictions in balance recovery following pelvis perturbations during human walking

In many simple walking models foot placement dictates the center of pressure location and ground reaction force components, whereas humans can modulate these aspects after foot contact. Because of the differences, it is unclear to what extend predictions made by models are valid for human walking. Yet, both model simulations and human experimental data have previously indicated that the center of mass (COM) velocity plays an important role in regulating stable walking.\ud \ud Here, perturbed human walking was studied for the relation of the horizontal COM velocity at heel strike and toe-off with the foot placement location relative to the COM, the forthcoming center of pressure location relative to the COM, and the ground reaction forces. Ten healthy subjects received various magnitude mediolateral and anteroposterior pelvis perturbations at toe-off, during 0.63 and 1.25 m s−1 treadmill walking.\ud \ud At heel strike after the perturbation, recovery from mediolateral perturbations involved mediolateral foot placement adjustments proportional to the mediolateral COM velocity. In contrast, for anteroposterior perturbations no significant anteroposterior foot placement adjustment occurred at this heel strike. However, in both directions the COM velocity at heel strike related linearly to the center of pressure location at the subsequent toe-off. This relation was affected by the walking speed and was, for the slow speed, in line with a COM velocity based control strategy previously applied by others in a linear inverted pendulum model. Finally, changes in gait phase durations suggest that the timing of actions could play an important role during the perturbation recovery

Responding to Major Burn Disasters in Resource-Limited Settings: Lessons Learned From an Oil Tanker Explosion in Nakuru, Kenya.

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Phase behavior of symmetric rod-plate mixtures revisited: Biaxiality versus demixing

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Optical response of silver nanoneedles on a mirror

Plasmonic properties of metal nanostructures are appealing due to their potential to enhance photovoltaics or sensing performance. Our aim was to identify the plasmonic characteristics of silver nanoneedles on a reflective layer in the polarized optical response. Experimental ellipsometry results are complemented by finite-difference time-domain (FDTD) calculations. Plasmon resonances on the nanoneedles can indeed be observed in the polarized optical response. This study reveals the details of the complex antenna-like behaviour of the nanoneedles which gives an agreement between experiment and FDTD simulation. The simulations show that the plasmon resonances lead to an effective negative refractive index, originating from the negative refractive index of the nanoneedles in combination with its supporting substrate, i.e. a mirror. This original study of a complex plasmonic system by ellipsometry and FDTD has great relevance for applications, making use of intricate light matter interaction

Stimulating job crafting behaviors of older workers:The influence of opportunity-enhancing human resource practices and psychological empowerment

Since job crafting behaviour is of profound importance for the retention of older workers, we examined how organizations can stimulate job crafting behaviour among older workers with opportunity-enhancing Human Resource (HR) practices. We introduced three job crafting behaviours: accommodative, utilization, and developmental job crafting. We hypothesized that opportunity-enhancing HR practices increase psychological empowerment among older workers and therefore their job crafting behaviour. We conducted a survey study with two waves among 125 Dutch older workers (65+) affiliated with a temporary employment agency aiming to employ older workers and found that changes in perceptions of opportunity-enhancing HR practices are positively related to changes in psychological empowerment and, in turn, to changes in utilization and developmental crafting behaviours. Unexpectedly, changes in psychological empowerment were not associated with changes in accommodative crafting and changes in opportunity-enhancing HR practices perceptions were not directly associated with changes in job crafting behaviour. With this study, we contribute to the literature on job crafting and human resource management by showing that opportunity-enhancing HR practices influence job crafting behaviour through psychological empowerment