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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5

Defect-Free Growth of Decagonal Quasicrystals around Obstacles

Quasicrystals are aperiodic solids with exotic physical properties. The mechanisms driving their growth are far from understood, particularly in the presence of rigid obstacles. Here, using in situ synchrotron x-ray tomography and molecular dynamics simulations, we investigate the interaction between decagonal quasicrystals and obstacles (shrinkage pores) during solidification of an Al 79 ⁢Co 6 ⁢Ni 15 alloy. The results reveal defect-free quasicrystal growth around the pores, independent of pore size and geometry. Our findings point to a universal feature of aperiodic solids: their ability to accommodate structural disruptions due to additional (phasonic) degrees of freedom. This Letter opens new possibilities for synthesizing large-scale, single quasicrystals from a liquid metal precursor.

alloys↗

Reversible, irreversible, and mixed regimes for periodically driven disks in random obstacle arrays

We examine an assembly of repulsive disks interacting with a random obstacle array under a periodic drive and find a transition from reversible to irreversible dynamics as a function of drive amplitude or disk density. At low densities and drives, the system rapidly forms a reversible state where the disks return to their exact positions at the end of each cycle. In contrast, at high amplitudes or high densities, the system enters an irreversible state where the disks exhibit normal diffusion. Between these two regimes, there can be an intermediate irreversible state where most of the system is reversible, but localized irreversible regions are present that are prevented from spreading through the system due to a screening effect from the obstacles. Here, we also find states that we term “combinatorial reversible states” in which the disks return to their original positions after multiple driving cycles. In these states, individual disks exchange positions but form the same configurations during the subcycles of the larger reversible cycle.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

ObstacleSense: Low-Power Neuromorphic Vision for Corridor Obstacle Awareness in Low-Level ADAS

The automotive industry’s pursuit of Level 5 autonomy is constrained by substantial perception-compute power requirements, often reaching 1, 000 + watts in full autonomy stacks. Reducing this energy burden requires rethinking perception not only at the high-end autonomy level, but also at the foundational Advanced Driver Assistance Systems (ADAS) level where low-power, safety-critical sensing can have broad impact. Neuromorphic vision provides a promising starting point: HD Dynamic Vision Sensors (DVS) can operate below 100 mW at the sensor level by reporting only asynchronous brightness changes. However, low-power sensing alone is insufficient if downstream perception reintroduces dense, energy-intensive computation. In particular, many event-driven object-detection pipelines still rely on CNN backbones, while purely spiking alternatives often trade away accuracy or ignore deployment constraints. We introduce ObstacleSense, a highly compact, CNN-free hybrid ANN–SNN framework for Level 0–1 forward-corridor obstacle awareness. Instead of performing full-scene object detection with a convolutional feature backbone, ObstacleSense targets the safety-critical question of whether the ego corridor is occupied and how far the nearest obstacle is. The architecture combines polarity-conditioned event encoding, lightweight temporal spiking dynamics, axial spatial mixing, and coarse-to-fine range estimation within a regular fixed-grid compute pattern. This design avoids the dense CNN backbone commonly used in event-based detection while maintaining a small state footprint suitable for eventual small-FPGA deployment. Before hardware mapping, we evaluate the software implementation using a model-side power proxy derived from MACs, weight and activation traffic, and spiking state updates under shared FP16 assumptions. On simulated CARLA event corpora, the deployment-oriented model achieves 0.9464 objectness F1, 0.9978 grid-level mAP, and 0.8987 m distance Mean Absolute Error at an estimated 1.92 mW proxy cost, while maintaining performance on unseen generalization test sequences.

Johnson-Scott, Zac [ORNL]↗

Effects of buried obstacles on penetration resistance in cohesionless soils

Recent experiments concerning penetration of cohesionless soils in special molds that include solid obstacles embedded within the soil matrix are reported. The relative effects of these obstacles with respect to the soil properties of relative density, texture, and gradation are also discussed. Because lunar soil is fairly cohesionless, special attention was given to the Apollo lunar simulant, AP-12.

Deluca, E. W.↗

Simulation of obstacle detection scheme for Mars terrain using minicomputer

Simulation for detection of obstacles on Martian terrain by a laser rangefinder mounted on an autonomous roving vehicle is achieved by a rapid estimation scheme on a computer with IDIIOM display. Near and far edges of pyramids and hemispherical craters or boulders can be recognized if the obstacles are more than about 15 m from the laser rangefinder and the noise standard deviation is less than about 10 cm. If these conditions are not met the rapid estimation scheme can still detect the top edge of a boulder and the near edge of a crater. The scheme is considered equivalent or better than an earlier (Reed, Sanyal, and Shen, 1974) four-directional Laplacian method, but requires slightly more computation.

Leung, K. L.↗

Obstacle detection by rapid estimation scheme with data scaling

A data scaling technique is proposed to improve the performance of a rapid estimation scheme for analyzing rover rangefinder data in the specific area of obstacle outline characterization. The scaling transformation involves multiplying the measured beam length times a scale factor and taking the logarithm in a certain base. Although analysis shows that introducing the scaling transformation has no primary effect on the detection ability and that there is no apparent signal-to-noise ratio improvement, computer simulations show a reduction in the number of false jumps. In the 40-m range the use of data scaling cleared the foreground of obstacles of noise and obtained definition of the near edge of a crater.

Marynowski, R. C.↗

Turbulent boundary layer around a group of obstacles in the direction of flow

Results of an investigation of a boundary layer in a turbulent flow on the surface of a wall having a group of obstacles on the path of flow are presented with regard to the mean velocity field, velocity distribution of the two dimensional flow, wall surface shear stresses and Reynolds stresses measured in a downstream cross section where an interference of boundary layers takes place in a flow around adjacent obstacles arranged on the path of flow.

Nakamura, I.↗

Application of a global solar wind/planetary obstacle interaction computational model: Earth, Venus, Mars, Jupiter and Saturn studies

This work relates to a series of collaborative investigations involving the application of a computational model for the determination of the detailed plasma and magnetic field properties associated with the global interaction of the solar wind with various planetary obstacles throughout the solar system. The theoretical method is based on an established single fluid, steady, dissipationless, magnetohydrodynamic continuum model, and is appropriate for the calculation of supersonic, super-Alfvenic solar wind flow past planetary obstacles. The investigations undertaken relate to studies of various solar wind interaction phenomena with Venus, Earth, Jupiter, and Saturn.

Stahara, S. S.↗

The location of the subsolar bow shock of Venus - Implications for the obstacle shape

The rise in periapsis altitude with time has allowed the Pioneer Venus spacecraft to begin probing the subsolar Venus bow shock. This has allowed the altitude of the subsolar bow shock to be determined by in situ observations for the first time. The observed altitude of 2280 km at the nose together with the previously determined terminator altitude can be used to infer the shape of the obstacle using the gasdynamic model of the solar wind interaction with Venus. When this shape is compared to the measured locations of the Venus ionopause (defined as the point where the magnetosheath magnetic field pressure and ionospheric thermal pressures are equal), it is found that the observed ionopause position is too low to qualify as the obstacle. It is inferred that a layer of the mass loaded plasma in the magnetosheath forms the magnetic barrier.

Russell, C. T.↗

Magnetic configurations of planetary obstacles

The interaction of the solar wind with planetlike obstacles is examined. The four different types of interactions, and the properties of the planets relative to their roles as obstacles to solar wind flow are discussed. The characteristic features of the magnetosphere of Mercury, Jupiter, Saturn, and the earth are described; particular attention is given to the configuration of the magnetosphere and the factors which control the position and shape of the magnetopause. The role of the magnetic field as it becomes modified in the solar wind interaction with nonmagnetic objects possessing an ionosphere is studied and examples of ionospheric interaction, such as Venusian and Titan interactions, are presented.

Lepping, R. P.↗

Path Planning with obstacle avoidance

The research report here summarizes a solution for two dimensional Path Planning with obstacle avoidance in a workspace with stationary obstacles. The solution finds the shortest path for the end effector of a manipulator arm. The program uses an overhead image of the robot work space and the starting and ending positions of the manipulator arm end effector to generate a search graph which is used to find the shortest path through the work area. The solution was originally implemented in VAX Pascal, but was later converted to VAX C.

Krause, Donald M.↗

Global time optimal motions of robotic manipulators in the presence of obstacles

A practical method to obtain the global time optimal motions of robotic manipulators is presented. This method takes into account the nonlinear manipulator dynamics, actuator constraints, joint limits, and obstacles. Previously developed methods of optimizing manipulator motions along given paths and a local path optimization are utilized. A set of best paths is obtained first in a global search over the manipulator workspace, using graph search and hierarchical pruning techniques. These paths are used as initial conditions for a continuous path optimization to yield the global optimal motion. Examples of optimized motions of a six-degree-of-freedom manipulator, operating in a three-dimensional space with obstacles, are presented.

Shiller, Zvi↗

Integration of active and passive sensors for obstacle avoidance

The automatic obstacle-avoidance guidance problem is studied under the operational constraints imposed by the rotorcraft nap-of-the-earth (NOE) environment. The problem is discussed for two different circumstances. The first assumes that a full range map is available, irrespective of the type of sensor being used. Two approaches are proposed to extend a two-dimensional obstacle-avoidance concept presented by Cheng (1988). The situation where only a sparse range map is available from a passive sensor is also treated. An integrated approach that augments the passive sensor with an active one is discussed, along with the problem of data fusion and how it is affected by the characteristics of NOE flight.

Cheng, Victor H. L.↗

Vision-based optimal obstacle-avoidance guidance for rotorcraft

An optimal guidance scheme for vision-based obstacle avoidance is developed. The proposed approach is useful for automating low-altitude rotorcraft flight. It explicitly accounts for the discrete nature of range information available from vision-based sensors and uses a linear combination of flight time, square of the vehicle acceleration and the square of the distance to various sensed obstacles as the performance index. A sixth-order, three-degree-of-freedom nonlinear point-mass vehicle model is included in the analysis. Numerical results using a sample image sequence is given.

Menon, P. K. A.↗

MHD flow past an obstacle - Large-scale flow in the magnetosheath

As a step to the study of the large-scale flow in the magnetosheath, the MHD flow past an obstacle is investigated. A time asymptotic method is used to obtain 3D steady-state solutions. The results indicate the formation of a depletion layer near the obstacle due to the increase of the magnetic field. Along the earth-sun line the plasma density increases first and then decreases from the post bow shock to the magnetopause. The local density maximum in front of the magnetopause may correspond to what was recently observed. When the interplanetary magnetic field direction is tilted from the solar wind flow, the IMF influences the shape of the bow shock as well as the location of the stagnation point at the magnetopause in a way consistent with observation. In addition, the results show the existence of a magnetosheath current in the post parallel-shock region.

Wu, C. C.↗

Potential-Field Scheme For Avoidance Of Obstacles By A Robot

Software for guidance of robot to operate in plant-growth chamber provides for end effector of robot to avoid obstacles at known positions. Includes algorithm implementing potential-field method for guidance away from obstacles and toward goal point, where object manipulated by end effector may be located.

Wegerif, Dan↗

Large-eddy simulation of turbulent flow in a channel with a surface-mounted two-dimensional obstacle using a dynamic subgrid-scale model

We apply the dynamic subgrid-scale model (DSGSM) to large-eddy simulation (LES) of turbulent channel flow with a square rib mounted on one wall. The Reynolds number (Re) is 3210 based on the mean velocity above the obstacle and the obstacle height. Near-wall structures are resolved with the no-slip boundary condition. The results show better agreement with direct numerical simulation (DNS) than LES with a fixed model constant, verifying the value of the DSGSM for simulating complex turbulent flows.

Yang, Kyung-Soo↗

The use of CMAC neural architectures in obstacle avoidance

In this paper, CMAC neural architectures are used in conjunction with a hierarchical planning approach to find collision free paths over two dimensional analog valued obstacle fields. The method constructs a coarse resolution version of the original problem and then finds the corresponding coarse optimal path using multipass dynamic programming. CMAC artificial neural architectures are used to estimate the analog transition costs that dynamic programming requires. The coarse optimal path is then used as a baseline for the construction of a fine scale optimal path through the original obstacle array.

Peterson, James K.↗