Naval Research Laboratory Spacecraft Engineering Division

Most events are processed by a number of neural pathways. These pathways often differ considerably in processing speed. Thus, coherent perception requires some form of synchronization mechanism. Moreover, this mechanism must be flexible, because neural processing speed changes over the life of an organism. Here we provide behavioral evidence that humans can adapt to a new intersensory temporal relationship (which was artificially produced by delaying visual feedback). The conflict between these results and previous work that failed to find such improvements can be explained by considering the present results as a form of sensorimotor adaptation.

Here we consider the problem of path planning for a hybrid fuel Unmanned Aerial Vehicle (UAV), equipped with both a battery and gasoline generator as two sources of energy. Routing the vehicle while considering this setup adds fuel constraints in addition to requiring the power source state to be specified along each edge along the path. We further add noise restrictions to the problem where certain edges (corresponding to certain portions of the path) have the restriction that the gasoline generator cannot be run. A solution to this path planning problem entails both a sequence of nodes, being the plain path the vehicle travels, and a sequence of values specifying the power source along each edge in the path. There is no work in the current literature regarding such a problem, with little at all concerning general planning or routing for hybrid fuel UAVs. Here, hybrid fuel UAV routing problem with noise restrictions is presented. The problem is first formulated as an Mixed Integer Linear Program. Then a dynamic programming algorithm is presented to solve the problem exactly. This algorithm is then compared to a branch-and-cut based method in terms of computational times for a variety of problem sizes. A case study is presented, using a graph which location data from an area surrounding an airport to produce goal nodes and noise restrictions to display the problem itself as well as the performance of the dynamic programming algorithm in a realistic scenario for this problem.

We present an improved heater design for thermionic cathodes using a rhenium filament encased in a boron nitride ceramic sleeve. This heater is relatively simple to fabricate, yet has been successfully used to reliably and repeatably light a lanthanum hexaboride (LaB6) hollow cathode based on a previously published design without noticeable filament degradation over hundreds of hours of operation. The high decomposition temperature of boron nitride (2800 C for inert environments) and melting point for rhenium (3180 C) make this heater especially attractive for use with LaB6, which may require operating temperatures upwards of 1700 C. While boron nitride decomposes in air above 1000 C, the heater was used only at vacuum with an inert gas discharge, and no degradation was observed. Limitations of current state of the art cathode heaters are also discussed and compared with the rhenium-boron nitride combination.

The authors discuss the antenna test range at the US Naval Ocean Systems Center, which provides solutions to some formidable electromagnetics problems on ships. They describe the measurement approach; the pattern range, a 160 ft diameter ground plane constructed of prestressed concrete covered with a very thin coating of lead; the impedance range, which has a subterranean instrument room that houses the measurement equipment and personnel during the test; and the time-domain measurement range. The authors then examine computer modelling of antennas and analysis of the EMC (electromagnetic compatibility) problem. The modelling approach as presented is not limited to ships; it can work for power lines, buildings, and even mountains.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Provides closed-form equations parameterizing the C/sup 2/ smooth path that globally minimizes the Euclidean norm of a robot's peak base reaction force while avoiding obstacles during 3D maneuvers in a gravity-free environment. Also, describes a computationally efficient technique that leads to a path typically having a peak force within 5% of the optimal path. The equations used to define the robot's motion are formulated after mapping the initial configuration, final (or goal) Cartesian location, and obstacles into a new space, the center of mass (CM) space. This is a Cartesian-like space that allows direct application of many existing control techniques, such as resolved rate control. In the CM space, a series of path segments guide the robot around the obstacles. Solving a system of equations based on these segments for boundary condition dependent constants determines the path. Currently, closed-form equations are unavailable for the boundary dependent constants, preventing exact determination of the globally optimal path. This paper introduces a procedure for locating the optimal path. Its final step uses sequential quadratic programming to locate boundary dependent constants. The equation formulations assume that the initial configuration of the robot is known and that the robot mass and obstacle positions are constant during the maneuver. The method developed has direct applicability to redundant and nonredundant robots. A detailed example, based on a nonredundant robot avoiding a single obstacle, illustrates the concepts presented.

In 1994, the Avionics Directorate of Wright Laboratory formed an Information Fusion Working Group (IFWG) to examine current fusion work, and identify future directions that the directorate should pursue in the fusion area. One of the recommendations the IFWG made was to develop an open modular avionics information fusion architecture. This paper focuses on this topic. It describes some of the issues associated with the development of an avionics fusion architecture and culminates into a description of a current avionics information fusion architecture design. This fusion architecture design is based on the four level fusion model that was defined by the Joint Director of Laboratories (JDL) Data Fusion Sub-panel. The main aim is to develop an open fusion architecture that will allow system designers the capability to re-use existing fusion algorithms.

Abstract The first step in implementing an intelligent ship is designing the ship intelligently. Naval ship design is becoming an interactive process where designers on different sites can work collaboratively and simultaneously, connected through virtual design environments. In this paper we introduce two such design environments. The first is an immersive, virtual reality environment enabling rapid design of ship space arrangements, exploration of Human System Integration issues, and reduced cost of test and evaluation through the use of modeling and simulation. The second is a systems engineering application capable of evaluating the benefit of spiral technology insertions, identifying areas for research and development investment, and evaluating the performance, risk, and affordability of proposed technologies in current and future ship systems, by conducting trade space analysis and optimization. Applications of these tools will be discussed.

The capillary pumped loop (CPL) is a passively pumped two-phase heat transport device that has demonstrated performance capabilities up to an order of magnitude greater than heat pipes, which are the current state-of-art. CPL technology has been developed to a near ready state for use as a thermal control device for advanced spacecraft systems. To further improve CPL performance, on a system level, the pumping head generated within the wick material must be enhanced. Utilizing the effect of a phenomenon known as liquid extraction (or EHD pumping); the Electrohydrodynamic (EHD) technique can effectively improve the liquid pumping capacity in a CPL system. EHD uses an electric field that can collect, guide, and pump liquid to the evaporating surface. This paper presents an experimental investigation of the feasibility of using EHD technology for improving CPL performances. The experimental study included EHD-enhanced pumping across a felt material that simulated a CPL wick. The results show more than 80% increase in heat transfer coefficients at the evaporator wick, with R-123 as the working fluid. Calculations, using the experimental data, demonstrate substantial increase in the corresponding additional pressure head developed across the wick through EHD effects.

Possible performance gains and cost reductions available through the evolution of succeedingly larger unmanned, and then manned, orbital transfer vehicles (OTV) as Shuttle upper stages are projected. Future missions could include delivery of 10,000 lb to GEO, planetary missions in the 2000-12,000 lb class, 30-42 ft payloads in the 5000-10,000 lb class, and manned and unmanned satellite servicing by the turn of the century. The vehicles could evolve from the Centaur F vehicle through stages of all-propulsive configurations to aerobraked, fully reusable vehicles. Reusability introduces cost savings and the ability to make plane changes. Furthermore, aerobraking will double the payload capability for round trip journeys to GEO, bringing costs down to $7000/lb.

Abstract Aiming at the practical problems of low detection accuracy and low detection speed for the detection of power insulators and insulator defects in a complex environmental context, a method is proposed to improve the YOLOv4 algorithm for the detection of power insulator images and insulators with defects. By making a dataset of electric power insulators and insulators with defects, the K-means algorithm is used to cluster the electric power insulator image samples to obtain different sizes of prior box parameters; then a weighting factor is introduced by improving the balanced cross-entropy to increase the contribution degree of the loss function; finally, the depth of the network is deepened by adding convolution layers before and after the spatial pyramidal pooling structure. The experimental results show that the single detection time of the improved model is 3.27S, and the average detection accuracy for insulator defects is improved by 24.36% compared with the original YOLOv4 algorithm. Also the value of the mean average accuracy on the test set by the improved YOLOv4 algorithm is 84.05%, which is 17.83% better than the original YOLOv4 algorithm, fully demonstrating the ability to locate and identify the defects existing in power insulator images well.

Database parameter tuning has always been a research hotspot. In recent years, there have been some efforts emerging to tune the runtime parameters of the cloud database by leveraging the high-dimensional space search ability of reinforcement learning. However, the previous solutions either train a tuning model for each database from scratch online, or use offline workloads that deviate greatly from the actual workload for model training, resulting in expensive training costs and poor tuning effect, which fails to meet the requirements of cloud database automatic tuning. In this paper, we propose a cloud database parameter tuning approach JWFCT. By providing a set of offline pre-training models instead of one, and combining with the workload classification and prediction technologies, the optimal configuration is determined with the tuning model that best matches the database workload characteristics, thus the tuning performance can be greatly improved. In addition, the models are also fine-tuned periodically based on online data that can further improve the performance. Experimental results show that JWFCT can significantly improve the throughput of the cloud database and reduce the recommendation time.

The capillary pump loop (CPL) is the current state-of-the-art space cooling system. It provides higher cooling capacity than most heat pipes, more installation flexibility, and much greater distance of heat transport due to the small diameter of wickless transport lines. Major disadvantages of the CPL include long and complicated startup procedures and the possibility of depriming at high heat input and load variation. The presented work was an experimental study to characterize the startup process for an EHD-assisted CPL system. Startup is achieved by an almost stable differential pressure and average temperature at the evaporator wall. When the electric field is applied, it interacts with the vapor/liquid distribution inside the core and the wick. It also provides an additional pumping effect of liquid to the evaporator surface. As a result, less time is needed to build up the meniscus. Furthermore, the instability-induced EHD pumping at liquid-vapor interface pushes the liquid-vapor interface near the evaporator wall to enhance the phase-change. These EHD-enhanced mechanisms collaborate to reduce the required duration at different regimes and hence realize the EHD-reducing startup time for a CPL system. Experimental data showed that about 50% startup time, reduction was attainable.

The number of extraneous touches, or number of user touches on a Touch Screen Display (TSD) that were in excess of the minimum required to perform a procedural task, was investigated as an implicit usability metric during a usability study. Data for this pilot study were obtained from a usability assessment performed to evaluate old and new versions of a TSD for adjusting system configuration settings on a system for the US Navy. Participants ( N = 28) performed a training mission on a gunnery trainer, during which they engaged simulated enemy boats while being interrupted to perform procedural tasks on a TSD at regular intervals. The count of extraneous touches was significantly correlated with task completion time and System Usability Scale (SUS) scores, providing notional support for its use as a usability metric. The advantages of this metric and limitations of these findings are discussed.

This paper proposes a novel synchronization algorithm for MIMO-OFDM system .It is applicable to the conditions where all the transmit antennas have different delays,and has an even broader sense.Therefore it can be used in the distributed MIMO systems.

Currently, distributed message systems (DMSs) are widely used in large-scale systems to assist system functionality and continuously bring performance benefits. Usually, the performance of a DMS system is highly dependent on its parameter configuration. However, due to its hundreds of parameters far beyond manual labor, default configurations are usually adopted, resulting in poor performance. The previous DMS configuration tuning proposals suffer from long tuning times due to the huge search space. To address this issue, this paper proposes an efficient DMS configuration automatic tuning scheme named DCT-HK, that can achieve tuning goals within a limited time budget. The key design is to leverage the historical tuning knowledge to reduce search space, thereby the time cost to find the optimal configuration can be significantly reduced. The experimental results validate the effectiveness of DCT-HK. Under the same tuning time budget, our scheme achieves better tuning performance than baseline methods.