Opportunistic sampling-based active visual SLAM for underwater inspection

This paper reports on an active SLAM framework for performing large-scale inspections with an underwater robot. We propose a path planning algorithm integrated with visual SLAM that plans loop-closure paths in order to decrease navigation uncertainty. While loop-closing revisit actions bound the robot’s uncertainty, they also lead to redundant area coverage and increased path length. Our proposed opportunistic framework leverages sampling-based techniques and information filtering to plan revisit paths that are coverage efficient. We employ Gaussian process regression for modeling the prediction of camera registrations and use a two-step optimization procedure for selecting revisit actions. We show that the proposed method offers many benefits over existing solutions and good performance for bounding navigation uncertainty in long-term autonomous operations with hybrid simulation experiments and real-world field trials performed by an underwater inspection robot.     

The personal lift-assist device and lifting technique: a principal component analysis

The personal lift-assist device (PLAD) is a non-motorised, on-body device that acts as an external force generator using the concept of stored elastic energy. In this study, the effect of the PLAD on the lifting kinematics of male and female lifters was investigated using principal component analysis. Joint kinematic data of 15 males and 15 females were collected using an opto-electronic system during a freestyle, symmetrical-lifting protocol with and without wearing the PLAD. Of the 31 Principal Components (PCs) retained in the models, eight scores were significantly different between the PLAD and no-PLAD conditions. There were no main effects for gender and no significant interactions. Results indicated that the PLAD similarly affected the lifting kinematics of males and females; demonstrating significantly less lumbar and thoracic flexion and significantly greater hip and ankle flexion when wearing the PLAD. These findings add to the body of work that suggest the PLAD may be a safe and effective ergonomic aid. STATEMENT OF RELEVANCE: The PLAD is an ergonomic aid that has been shown to be effective at reducing low back demands during manual materials handling tasks. This body of work establishes that the PLAD encourages safe lifting practices without adversely affecting lifting technique.     

Test-retest reliability of Purdue Pegboard performance in thermoneutral and cold ambient conditions

In the cold, Purdue Pegboard (PP) performance declines. The purpose of this study was to determine if this cold-induced impairment is consistent across days (i.e. test-retest reliability) in 5°C. In thermoneutral air (25°C), 14 men were familiarised to the dominant hand (PPa) and bimanual (PPb) PP tasks. They then experienced two 90-min cold exposures (Day 1, Day 2) while wearing ～1 clo. Bare hands were maintained throughout. Performance on both tasks showed high reliability from day to day (intraclass correlations >0.700) in both thermoneutral and cold conditions. However for both tasks, room temperature performance did not predict performance in the cold (intraclass correlations <0.450). When screening applicants for manual labour in the cold, one must consider that room temperature dexterity does not correlate with dexterity in the cold. It is recommended that a 60-min period of cold exposure be employed to assess manual dexterity in these workers. STATEMENT OF RELEVANCE: This study shows that PP performance in room temperature does not predict performance in the cold but performance in the cold is consistent from day to day. When screening applicants for manual labour in the cold, it is recommended that dexterity tests be conducted in the same ambient conditions.     

Discrete‐time low‐gain control of linear systems with input/output nonlinearities

Discrete‐time low‐gain control strategies are presented for tracking of constant reference signals for finite‐dimensional, discrete‐time, power‐stable, single‐input, single‐output, linear systems subject to a globally Lipschitz, non‐decreasing input nonlinearity and a locally Lipschitz, non‐decreasing, affinely sector‐bounded output nonlinearity (the conditions on the output nonlinearities may be relaxed if the input nonlinearity is bounded). Both non‐adaptive and adaptive gain sequences are considered. In particular, it is shown that applying error feedback using a discrete‐time ‘integral’ controller ensures asymptotic tracking of constant reference signals, provided that (a) the steady‐state gain of the linear part of the plant is positive, (b) the positive gain sequence is ultimately sufficiently small and (c) the reference value is feasible in a very natural sense. The classes of input and output nonlinearities under consideration contain standard nonlinearities important in control engineering such as saturation and deadzone. The discrete‐time results are applied in the development of sampled‐data low‐gain control strategies for finite‐dimensional, continuous‐ time, exponentially stable, linear systems with input and output nonlinearities. Copyright © 2001 John Wiley & Sons, Ltd.     

The aDORe federation architecture: digital repositories at scale

The need to federate repositories emerges in two distinctive scenarios. In one scenario, scalability-related problems in the operation of a repository reach a point beyond which continued service requires parallelization and hence federation of the repository infrastructure. In the other scenario, multiple distributed repositories manage collections of interest to certain communities or applications, and federation is an approach to present a unified perspective across these repositories. The high-level, 3-Tier aDORe federation architecture can be used as a guideline to federate repositories in both cases. This paper describes the architecture, consisting of core interfaces for federated repositories in Tier-1, two shared infrastructure components in Tier-2, and a single-point of access to the federation in Tier-3. The paper also illustrates two large-scale deployments of the aDORe federation architecture: the aDORe Archive repository (over 100,000,000 digital objects) at the Los Alamos National Laboratory and the Ghent University Image Repository federation (multiple terabytes of image files).     

Improved Positioning Accuracy of the PA10-6CE Robot with Geometric and Flexibility Calibration

Accurate determination of robot geometric and flexibility parameters permits significant reduction of systematic errors and improved end-effector positioning accuracy. We apply a 30-parameter flexible geometric model to the Mitsubishi PA10-6CE robot and reduce mean/peak positional errors from 1.80/2.45 mm to 0.33/0.71 mm while loaded at 44 N.     

Discrete retardance second harmonic generation ellipsometry

A new instrument was constructed to perform discrete retardance nonlinear optical ellipsometry (DR-NOE). The focus of the design was to perform second harmonic generation NOE while maximizing sample and application flexibility and minimizing data acquisition time. The discrete retardance configuration results in relatively simple computational algorithms for performing nonlinear optical ellipsometric analysis. NOE analysis of a disperse red 19 monolayer yielded results that were consistent with previously reported values for the same surface system, but with significantly reduced acquisition times.     

Solid state reaction in sandwich-type Al/Cu thin films

Al/Cu/Al and Cu/Al/Cu triple layers with approximately 10 nm single layer thickness deposited on tungsten substrates were analyzed in the early stages of reactive interdiffusion by means of atom probe tomography. The first reaction product is found after 5 min thermal treatment at 110 degrees C and identified by direct chemical analysis to be Al2Cu. Surprisingly, we found a significant asymmetry in the reaction rate of the new phase with the stacking sequence: the thickness of the product grown at the interfaces, at which Cu is deposited on top of the Al layer, is approximately 1.5-2 times thicker than the other one at the interfaces at which Al is deposited onto a Cu layer. On the other hand, at both interfaces the thickness of the product layer depends parabolically on time. No precursory interdiffusion and no distinct nucleation process of the product are observed.     

Measuring progress in Premo order-verification

Since verification of computational simulation codes requires significant resources, the ability to measure progress in verification is critical to assess whether resources are being applied appropriately. Additionally, potential users need to know what fraction of the software has been order-verified. In this study, the procedures and progress measures presented by Knupp et al. (Measuring progress order-verification within software development projects. Engineering with Computers, appears in this issue, 2007) are demonstrated on the Premo software, which simulates compressible aerodynamics through and around general geometries. Premo was selected for this demonstration because extensive order-verification tests have been previously performed, yet no systematic effort has been made to assess test-suite completeness or progress. This effort was performed to identify the practical issues encountered when attempting to apply the ideas by Knupp (Measuring progress order-verification within software development projects. Engineering with Computers, appears in this issue, 2007) to existing production-quality software. In this work, a non-specific order-verification exercise is considered, as opposed to an application-specific order-verification exercise, since past and present Premo order-verification efforts have been motivated by the need to verify all of the code, rather than portions relevant for specific applications. Constructing an order-verification test suite that verifies the order of accuracy of all the code capabilities is a major step in measuring progress. A practical approach to test-suite construction is described that helps create a complete test suite through a combination of coarse-grain code coverage, input-keyword inspection, discretization-algorithm documentation, and expert knowledge. Some of the difficulties and issues encountered during the construction of the test suite are described, along with recommendations on how to deal with them. Once the test suite is constructed, the progress measures proposed by Knupp (Measuring progress order-verification within software development projects. Engineering with Computers, appears in this issue, 2007) can be evaluated and used to reconstruct the history of progress in Premo verification over the past several years. Gaps in Premo verification are identified and indicate future directions for making progress. Additionally, a measure of Premo verification fitness is computed for selected applications commonly simulated in the aerospace industry. It is hoped that this demonstration will provide a practical example for other software-development groups in measuring their own verification progress. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.

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