2,547 research outputs found
Learning an Efficient Terrain Representation for Haptic Localization of a Legged Robot
Although haptic sensing has recently been used for legged robot localization
in extreme environments where a camera or LiDAR might fail, the problem of
efficiently representing the haptic signatures in a learned prior map is still
open. This paper introduces an approach to terrain representation for haptic
localization inspired by recent trends in machine learning. It combines this
approach with the proven Monte Carlo algorithm to obtain an accurate,
computation-efficient, and practical method for localizing legged robots under
adversarial environmental conditions. We apply the triplet loss concept to
learn highly descriptive embeddings in a transformer-based neural network. As
the training haptic data are not labeled, the positive and negative examples
are discriminated by their geometric locations discovered while training. We
demonstrate experimentally that the proposed approach outperforms by a large
margin the previous solutions to haptic localization of legged robots
concerning the accuracy, inference time, and the amount of data stored in the
map. As far as we know, this is the first approach that completely removes the
need to use a dense terrain map for accurate haptic localization, thus paving
the way to practical applications.Comment: This work has been submitted to the IEEE for possible publication.
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Comparison of measured and EF5-r derived NâO fluxes from a spring-fed river
There is considerable uncertainty in the estimates of indirect NâO emissions as defined by the Intergovernmental Panel on Climate Change's (IPCC) methodology. Direct measurements of NâO yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global NâO budget.
The objectives of this research were to measure the NâO fluxes from a spring-fed river, relate these fluxes to the dissolved NâO concentrations and NOââN loading of the river, and to try and define the indirect emission factor (EF5-r) for the river.
Gas bubble ebullition was observed at the river source with bubbles containing 7.9 ”L NâO Lâ»Âč. River NOââN and dissolved NâO concentrations ranged from 2.5 to 5.3 mg Lâ»Âč and 0.4 to 1.9 ”g NâO-N Lâ»Âč respectively with NâO saturation reaching 404%. Floating headspace chambers were used to sample NâO fluxes. NâOâN fluxes were significantly related to dissolved NâOâN concentrations (rÂČ = 30.6) but not to NOââN concentrations. The NâOâN fluxes ranged from 38-501 ”g mâ»ÂČ hâ»Âč, averaging 171 ”g mâ»ÂČ hâ»Âč (± Std. Dev. 85) overall. The measured NâOâN fluxes equated to an EF5-r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an over-estimate due to the degassing of antecedent dissolved NâO present in the groundwater that fed the river
Explaining the effectiveness of performance-based logistics: a quantitative examination
The article of record as published may be located at http://dx.doi.org/10.1108/09574091111181354Purpose â Performance-based logistics (PBL) strategies are providing governments and for-profit
organizations with a contractual mechanism that reduces the life cycle costs of their systems. PBL
accomplishes this by establishing contracts that focus on the delivery of performance not parts. PBL
establishes a metric based governance structure where suppliers make more profit when they invest in
logistics process improvements, or system redesign, that reduces total cost of ownership. While work
has been done to outline an overall PBL theoretical framework, the underlying theory explaining the
enablers that lead to organizational and team-level, team-goal alignment associated with the PBL
governance structure requires testing. The purpose of this paper is to quantitatively test previously
posited relationships between enablers of PBL and PBL effectiveness. An additional objective is to
explore any differences in PBL effectiveness between different business sectors.This material is based upon work supported by the Naval Postgraduate School Acquisition Research Program under Grant No. N00244-10-1-0074
Maximising carbonate content in sodium-carbonate Co-substituted hydroxyapatites prepared by aqueous precipitation reaction
Acknowledgments The authors would like to acknowledge the University of Aberdeen and the Royal Commission for the Exhibition of 1851 for providing financial support as well as Mr Colin Taylor and Mr John Still for their assistance in collecting some of the experimental data presented here.Peer reviewedPostprin
Potassiumâcarbonate co-substituted hydroxyapatite compositions : maximising the level of carbonate uptake for potential CO2Â utilisation options
The authors would like to acknowledge the University of Aberdeen and the Royal Commission for the Exhibition of 1851 for providing financial support.CO2 utilisation is a rapidly growing area of interest aimed at reducing the magnitude of anthropogenic greenhouse gas emissions. We report the synthesis of potassiumâcarbonate (KâCO3) co-substituted hydroxyapatites with potassium and carbonate contents ranging from approximately 0.4â0.9 wt% and 3.4â13.0 wt% respectively via an aqueous precipitation reaction between calcium hydroxide, phosphoric acid and either potassium carbonate or potassium hydrogenâcarbonate. The incorporated carbonate is situated on both hydroxyl and phosphate sites. A subsequent heat treatment in dry CO2 at 600 °C allowed for a KâCO3 co-substituted apatite containing approximately 16.9 wt% CO32â to be prepared, amongst the largest carbonate contents that have been reported for such a material to date. Although this work shows that KâCO3 co-substituted apatites with high levels of carbonate incorporation can be prepared using simple, room temperature, aqueous precipitation reactions with starting reagents unlikely to pose significant environmental risks, testing of these materials in prospective applications (such as solid fertilisers) is required before they can be considered a viable CO2 utilisation option. A preliminary assessment of the effect of potassium/carbonate substitution on the solubility of the as-prepared compositions showed that increasing carbonate substitution increased the solubility.Publisher PDFPeer reviewe
A System of Conservative Regridding for Ice-Atmosphere Coupling in a General Circulation Model (GCM)
The method of elevation classes, in which the ice surface model is run at multiple elevations within each grid cell, has proven to be a useful way for a low-resolution atmosphere inside a general circulation model (GCM) to produce high-resolution downscaled surface mass balance fields for use in one-way studies coupling atmospheres and ice flow models. Past uses of elevation classes have failed to conserve mass and energy because the transformation used to regrid to the atmosphere was inconsistent with the transformation used to downscale to the ice model. This would cause problems for two-way coupling. A strategy that resolves this conservation issue has been designed and is presented here. The approach identifies three grids between which data must be regridded and five transformations between those grids required by a typical coupled atmosphere-ice flow model. This paper develops a theoretical framework for the problem and shows how each of these transformations may be achieved in a consistent, conservative manner. These transformations are implemented in Glint2, a library used to couple atmosphere models with ice models. Source code and documentation are available for download. Confounding real-world issues are discussed, including the use of projections for ice modeling, how to handle dynamically changing ice geometry, and modifications required for finite element ice models
Fluctuations of an Atomic Ledge Bordering a Crystalline Facet
When a high symmetry facet joins the rounded part of a crystal, the step line
density vanishes as sqrt(r) with r denoting the distance from the facet edge.
This means that the ledge bordering the facet has a lot of space to meander as
caused by thermal activation. We investigate the statistical properties of the
border ledge fluctuations. In the scaling regime they turn out to be
non-Gaussian and related to the edge statistics of GUE multi-matrix models.Comment: Version with major revisions -- RevTeX, 4 pages, 2 figure
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