Apparent superballistic dynamics in one-dimensional random walks with biased detachment

The mean-squared displacement (MSD) is an averaged quantity widely used to assess anomalous diffusion. In many cases, such as molecular motors with finite processivity, dynamics of the system of interest produce trajectories of varying duration. Here we explore the effects of finite processivity on different measures of the MSD. We do so by investigating a deceptively simple dynamical system: a one-dimensional random walk (with equidistant jump lengths, symmetric move probabilities, and constant step duration) with an origin-directed detachment bias. By tuning the time dependence of the detachment bias, we find through analytical calculations and trajectory simulations that the system can exhibit a broad range of anomalous diffusion, extending beyond conventional diffusion to superdiffusion and even superballistic motion. We analytically determine that protocols with a time-increasing detachment lead to an ensemble-averaged velocity increasing in time, thereby providing the effective acceleration that is required to push the system above the ballistic threshold. MSD analysis of burnt-bridges ratchets similarly reveals superballistic behavior. Because superdiffusive MSDs are often used to infer biased, motor-like dynamics, these findings provide a cautionary tale for dynamical interpretation

George C. Marshall Space Flight Center Research and Technology Report 2014

Many of NASA's missions would not be possible if it were not for the investments made in research advancements and technology development efforts. The technologies developed at Marshall Space Flight Center contribute to NASA's strategic array of missions through technology development and accomplishments. The scientists, researchers, and technologists of Marshall Space Flight Center who are working these enabling technology efforts are facilitating NASA's ability to fulfill the ambitious goals of innovation, exploration, and discovery

The geometry of thermodynamic control

A deeper understanding of nonequilibrium phenomena is needed to reveal the principles governing natural and synthetic molecular machines. Recent work has shown that when a thermodynamic system is driven from equilibrium then, in the linear response regime, the space of controllable parameters has a Riemannian geometry induced by a generalized friction tensor. We exploit this geometric insight to construct closed-form expressions for minimal-dissipation protocols for a particle diffusing in a one dimensional harmonic potential, where the spring constant, inverse temperature, and trap location are adjusted simultaneously. These optimal protocols are geodesics on the Riemannian manifold, and reveal that this simple model has a surprisingly rich geometry. We test these optimal protocols via a numerical implementation of the Fokker-Planck equation and demonstrate that the friction tensor arises naturally from a first order expansion in temporal derivatives of the control parameters, without appealing directly to linear response theory

Evaluations of in-traffic performance of high-intensity discharge headlamps

This study evaluated subjects' impressions of performance of high-intensity discharge (HID) headlamps after in-traffic experience, with an emphasis on colour appearance of red stop signs. In the first of two tasks, subjects drove (or rode) for half an hour on a variety of roads in a car equipped with either HID or tungsten-halogen low-beam headlamps. Instructions did not mention colour appearance. The second task involved a direct comparison of HID and tungsten-halogen headlamps. In this task, subjects drove (or rode) twice along a 7-minute route in a residential area, and they were instructed to pay attention to the colour appearance of stop signs and other objects. The main finding from Task 1 is that subjects who experienced HID headlamps did not report more (or fewer) spontaneous negative comments on colour appearance of stop signs or other objects than did subjects who experienced tungsten-halogen headlamps. Furthermore, the evaluations of the overall performances of the two types of headlamps were not different. In the direct comparison of Task 2 there was no evidence of problems with colour appearance when using HID headlamps. Moreover, subjects preferred HID headlamps in terms of the overall performance, and in making stop signs and other objects stand out from their background. However, this preference for HID headlamps was present only for subjects who had the relatively extended exposure to the HID headlamps in Task 1. The present results provide no evidence for problems with colour appearance of stop signs and other objects when using HID headlamps. Furthermore, the study provides evidence that observers perceive HID headlamps as helping stop signs and other objects to stand out from their background. The results imply that given a somewhat extended exposure to HID headlamps, drivers would prefer them over current tungsten-halogen headlamps.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68417/2/10.1177_096032719402600402.pd

Marshall Space Flight Center Research and Technology Report 2015

The investments in technology development we made in 2015 not only support the Agency's current missions, but they will also enable new missions. Some of these projects will allow us to develop an in-space architecture for human space exploration; Marshall employees are developing and testing cutting-edge propulsion solutions that will propel humans in-space and land them on Mars. Others are working on technologies that could support a deep space habitat, which will be critical to enable humans to live and work in deep space and on other worlds. Still others are maturing technologies that will help new scientific instruments study the outer edge of the universe-instruments that will provide valuable information as we seek to explore the outer planets and search for life

Driver eye fixations and the optimal locations for automobile brake lights

This study evaluated the distributions of driver eye fixations when following other vehicles. The aim was to describe the areas of the forward field of view that are most frequently fixated. Such information is important for selecting optimal locations for automobile brake lights: Brake lights that are closer to eye fixations are likely to result in shorter driver reaction times than brake lights farther away from the fixations. A head-mounted, corneal-reflection device was used to monitor eye fixations. The data were collected during daylight hours in slow-moving urban traffic. A total of 3,600 eye fixations were analyzed for three different lead cars. The results indicate that, under the conditions of this study, the eye fixations tended to concentrate on the rear-window of the lead car and not in the neighborhood of the standard low-mounted brake lights. The results provide a possible behavioral explanation for the accident reductions found with high-mounted brake lights in previous field studies. Furthermore, high-mounted brake lights located at the edges of the vehicle might be even closer to eye fixations than a center-high-mounted brake light.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26203/1/0000283.pd