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Top 10 slowest
Discover facts and figures about the slowest things in the world! From the sleepy-seeming sloth to incredibly sluggish cars, find out what creeps into the slowest top ten ever.
Book
Correlation Between Speed of the Leader and Peak Current of the Return Stroke in Negative Lightning Flashes
This study analyzes the two‐dimensional speed profiles of 107 stepped leaders and 93 dart leaders recorded by high‐speed cameras in Utah (USA), together with data from lightning location system. The results shows that the final and average speed of the stepped leader has a very strong (R = 0.82) and strong (R = 0.71) correlation with the peak current of the return stroke. It also shows that 91% of the stepped leaders increased their speed near the ground (average increase of 69%). The same analysis for dart leaders shows weak correlation with the peak current of the prospective return stroke (R = 0.39 to average speed and R = 0.28 to final speed). This paper briefly discusses why peak current is better correlated with final speed than with the average speed, and why stepped leaders exhibit a significant correlation, while dart leaders do not. Plain Language Summary This study looks at how fast stepped leaders and dart leaders of lightning flashes propagate from the cloud base to ground, using high‐speed camera videos and data from a lightning location system. The results show that the final and average speed of the leaders are well correlated to the return stroke current, the return stroke current being more closely related to the final speed than the average speed. In contrast, dart leaders showed a weak correlation between their speed and the return stroke current. It also shows that most stepped leaders sped up as they got closer to the ground. Key Points The return stroke peak current is better correlated with final speed than with the average speed of the stepped leader No significant correlation was found between dart leaders speed and stroke peak current The stepped leaders increase their propagation speed near the ground
Journal Article
Top 10 fastest
Discover fascinating facts and figures about the speediest things in the world! From the super-fast Bugatti Veyron car to the fastest land animal, the cheetah, find out what the fastest things on the planet are.
Book
Optimal Motorway Traffic Flow Control Involving Variable Speed Limits and Ramp Metering
The impact of variable speed limits (VSL) on aggregate traffic flow behaviour on motorways is shown to bear similarities to the impact of ramp metering, in particular, when addressing potentially active bottlenecks. A quantitative model of the VSL impact is proposed that allows for VSL to be incorporated in a macroscopic second-order traffic flow model as an additional control component. The integrated motorway network traffic control problem involving ramp metering and VSL control measures is formulated as a constrained discrete-time optimal control problem and is solved efficiently even for large-scale networks by a suitable feasible direction algorithm. An illustrative example of a hypothetical motorway stretch is investigated under different control scenarios, and it is shown that traffic flow efficiency can be substantially improved when VSL control measures are used, particularly in integration with coordinated ramp metering.
Journal Article
Differences in Speed and Duration of Bird Migration between Spring and Autumn
It has been suggested that birds migrate faster in spring than in autumn because of competition for arrival order at breeding grounds and environmental factors such as increased daylight. Investigating spring and autumn migration performances is important for understanding ecological and evolutionary constraints in the timing and speed of migration. We compiled measurements from tracking studies and found a consistent predominance of cases showing higher speeds and shorter durations during spring compared to autumn, in terms of flight speeds (airspeed, ground speed, daily travel speed), stopover duration, and total speed and duration of migration. Seasonal differences in flight speeds were generally smaller than those in stopover durations and total speed/duration of migration, indicating that rates of foraging and fuel deposition were more important than flight speed in accounting for differences in overall migration performance. Still, the seasonal differences in flight speeds provide important support for time selection in spring migration.
Journal Article
Measuring speed
When a bird flies by a window or a car zooms by on the highway, we often wonder how fast the two objects traveled. This book explains the concept of speed to readers while showing them accessible ways to measure it for themselves. Learning the amount of distance traveled, and how quickly that distance was covered, is a great way to implement a variety of STEM topics while practicing this essential mathematical skill.
Book
Effects of the Reynolds number on train aerodynamics considering air compressibility: a wind tunnel study
The study of Reynolds number (Re) effects is crucial for optimizing train aerodynamics, enhancing safety and reducing energy consumption of high-speed trains. In this paper, a wind tunnel test was carried out to investigate the influence of Re on the train aerodynamic performance considering the shift of the air compressibility, which has not yet been explored to date. The test was conducted in a low-speed and large-scale tunnel with a stationary floor and the vehicle model was based on a 1/8th scaled train with three units. The Re ranges from 0.75 × 106∼3.12 × 106 by accelerating the uniform wind speed from U = 27.8 m/s to U = 115 m/s with zero-yaw. The Mach number (Ma) of the maximum speed scenario has exceeded 0.3, indicating that the airflow can be considered as being in the compressible range. The results show that the aerodynamic characteristics of high-speed trains exhibit a self-similarity region of Re, which is dependent on the flow velocity. The aerodynamic loads change little when Re ≥ 1.51 × 106, which corresponds to U ≥ 55.6 m/s. Therefore, the compressibility of the airflow within the range up to U = 115 m/s has a negligible effect on aerodynamic loads, and can thus be disregarded. However, the surface pressure significantly decreases when the incoming flow surpasses 0.3 Ma and transitions into a compressible state. While the compressibility has a relatively minor impact on macroscopic aerodynamics, it cannot be overlooked when considering detailed flow field, such as surface pressure.
Journal Article
Evaluations of Speed Camera Interventions Can Deliver a Wide Range of Outcomes: Causes and Policy Implications
Speeding (travelling at speeds above the speed limit) is proven to be a major contributor to serious crashes, and speed management interventions including speed cameras are shown to reduce speeds, crashes, and trauma. However, the present review identifies that the range of outcomes reported in evaluations of speed cameras is large, complicating the understanding of effects, and inviting scepticism about the value of speed cameras despite the large numbers of reported successes, as well as systematic reviews and meta-analyses that demonstrate their life- and injury-saving value. Therefore, this review is focused on the factors that contribute to the large range of findings, including reasons for genuine differences in the outcomes delivered by different camera programs and variations in evaluation methodology that influence the extent to which real benefits are detected. Finally, recommendations are offered to maximise the safety benefits of speed-camera programs (including ensuring the full chain of requirements for general deterrence is met; strong communications about new programs and expansions at least several weeks in advance of implementation; and unpredictability of enforcement versus signposted cameras) and to improve evaluation methods (especially around determining the road lengths/locations assumed to be treated by the cameras and use of control locations).
Journal Article