Source illusion devices for flexural Lamb waves using elastic metasurfaces

Metamaterials with the transformation method has greatly promoted the development in achieving invisibility and illusion for various classical waves. However, the requirement of tailor-made bulk materials and extreme constitutive parameters associated to illusion designs hampers its further progress. Inspired by recent demonstrations of metasurfaces in achieving reduced versions of electromagnetic cloaks, we propose and experimentally demonstrate source illusion devices to manipulate flexural waves using metasurfaces. The approach is particularly useful for elastic waves due to the lack of form-invariance in usual transformation methods. We demonstrate metasurfaces for shifting, transforming and splitting a point source with "space-coiling" structures. The effects are found to be broadband and robust against a change of source position, with agreement from numerical simulations and Huygens-Fresnel theory. The proposed approach provides an avenue to generically manipulate guided elastic waves in solids, and is potentially useful for applications such as non-destructive testing, enhanced sensing and imaging

Formation of sinuous ridges by inversion of river-channel belts in Utah, USA, with implications for Mars

Sinuous ridges are important landforms on the surface of Mars that show promise for quantifying ancient martian surface hydrology. Morphological similarity of these ridges to river channels in planform led to a hypothesis that ridges are topographically inverted river channels, or “inverted channels”, formed due to an erosion-resistant channel-filling material that preserved a snapshot of the channel geometry in inverted relief due to differential erosion. An alternative deposit-inversion hypothesis proposes that ridges represent exhumed river-channel belts, with geometries that reflect the lateral migration and vertical aggradation of rivers over significant geologic time, rather than the original channel geometry. To investigate these hypotheses we studied sinuous ridges within the Cretaceous Cedar Mountain Formation near Green River, Utah, USA. Ridges in Utah extend for hundreds of meters, are up to 120 m wide, and stand up to 39 m above the surrounding plain. Ridges are capped by sandstone bodies 3–10 m thick that contain dune- and bar-scale inclined stratification, which we interpret as eroded remnants of channel belts that record the migration and aggradation of single-thread, sand-bedded rivers, rather than channel fills that can preserve the original channel geometry. Caprocks overlie mudstones and thinner sandstone beds that are interpreted as floodplain deposits, and in cases additional channel-belt sandstones are present lower in the ridge stratigraphy. Apparent networks from branching ridges typically represent discrete sandstone bodies that cross at different stratigraphic levels rather than a coeval river network. Ridge-forming sandstone bodies also have been narrowed during exhumation by cliff retreat and bisected by fluvial erosion. Using a large compilation of channel-belt geometries on Earth and our measurements of ridges in Utah, we propose that caprock thickness is the most reliable indicator of paleo-channel geometry, and can be used to reconstruct river depth and discharge. In contrast, channel lateral migration and caprock erosion during exhumation make ridge breadth an uncertain proxy for channel width. An example in Aeolis Dorsa, Mars, illustrates that river discharge estimates based solely on caprock width may differ significantly from estimates based on caprock thickness. Overall, our study suggests that sinuous ridges are not inverted channel fills, but rather reflect exhumation of a thick stratigraphic package of stacked channel belts and overbank deposits formed from depositional rivers over significant geologic time

Validation of Envisat MERIS algorithms for chlorophyll retrieval in a large, turbid and optically-complex shallow lake

The 10-year archive of MEdium Resolution Imaging Spectrometer (MERIS) data is an invaluable resource for studies on lake system dynamics at regional and global scales. MERIS data are no longer actively acquired but their capacity for global scale monitoring of lakes from satellites will soon be re-established through the forthcoming Sentinel-3 Ocean and Land Colour Instrument (OLCI). The development and validation of in-water algorithms for the accurate retrieval of biogeochemical parameters is thus of key importance if the potential of MERIS and OLCI data is to be fully exploited for lake monitoring. This study presents the first extensive validation of algorithms for chlorophyll-a (chl-a) retrieval by MERIS in the highly turbid and productive waters of Lake Balaton, Hungary. Six algorithms for chl-a retrieval from MERIS over optically complex Case 2 waters, including band-difference and neural network architectures, were compared using the MERIS archive for 2007-2012. The algorithms were locally-tuned and validated using in situ chl-a data (n = 289) spanning the five year processed image time series and from all four lake basins. In general, both band-difference algorithms tested (Fluorescence Line Height (FLH) and Maximum Chlorophyll Index (MCI)) performed well, whereas the neural network processors were generally found to much less accurately retrieve in situ chl-a concentrations. The Level 1b FLH algorithm performed best overall in terms of chl-a retrieval (R2 = 0.87; RMSE = 4.19 mg m- 3; relative RMSE = 30.75%) and particularly at chl-a concentrations of ≥ 10 mg m- 3 (R2 = 0.85; RMSE = 4.81 mg m- 3; relative RMSE = 20.77%). However, under mesotrophic conditions (i.e., chl-a < 10 mg m- 3) FLH was outperformed by the locally-tuned FUB/WeW processor (relative FLH RMSE < 10 mg m- 3 = 57.57% versus relative FUB/WeW RMSE < 10 mg m- 3 = 46.96%). An ensemble selection of in-water algorithms is demonstrated to improve chl-a retrievals

Formation of sinuous ridges by inversion of river-channel belts in Utah, USA, with implications for Mars

Sinuous ridges are important landforms on the surface of Mars that show promise for quantifying ancient martian surface hydrology. Morphological similarity of these ridges to river channels in planform led to a hypothesis that ridges are topographically inverted river channels, or “inverted channels”, formed due to an erosion-resistant channel-filling material that preserved a snapshot of the channel geometry in inverted relief due to differential erosion. An alternative deposit-inversion hypothesis proposes that ridges represent exhumed river-channel belts, with geometries that reflect the lateral migration and vertical aggradation of rivers over significant geologic time, rather than the original channel geometry. To investigate these hypotheses we studied sinuous ridges within the Cretaceous Cedar Mountain Formation near Green River, Utah, USA. Ridges in Utah extend for hundreds of meters, are up to 120 m wide, and stand up to 39 m above the surrounding plain. Ridges are capped by sandstone bodies 3–10 m thick that contain dune- and bar-scale inclined stratification, which we interpret as eroded remnants of channel belts that record the migration and aggradation of single-thread, sand-bedded rivers, rather than channel fills that can preserve the original channel geometry. Caprocks overlie mudstones and thinner sandstone beds that are interpreted as floodplain deposits, and in cases additional channel-belt sandstones are present lower in the ridge stratigraphy. Apparent networks from branching ridges typically represent discrete sandstone bodies that cross at different stratigraphic levels rather than a coeval river network. Ridge-forming sandstone bodies also have been narrowed during exhumation by cliff retreat and bisected by fluvial erosion. Using a large compilation of channel-belt geometries on Earth and our measurements of ridges in Utah, we propose that caprock thickness is the most reliable indicator of paleo-channel geometry, and can be used to reconstruct river depth and discharge. In contrast, channel lateral migration and caprock erosion during exhumation make ridge breadth an uncertain proxy for channel width. An example in Aeolis Dorsa, Mars, illustrates that river discharge estimates based solely on caprock width may differ significantly from estimates based on caprock thickness. Overall, our study suggests that sinuous ridges are not inverted channel fills, but rather reflect exhumation of a thick stratigraphic package of stacked channel belts and overbank deposits formed from depositional rivers over significant geologic time

Manifesto for Teaching Online 2016

Tonina, Municipio Ocosingo, ChiapasOP III Structure F4-5, dalle avec trace de sciage

Protocol for a meta-research study of protocols for diet or nutrition-related trials published in indexed journals:general aspects of study design, rationale and reporting limitations

INTRODUCTION: The Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) reporting guideline establishes a minimum set of items to be reported in any randomised controlled trial (RCT) protocol. The Template for Intervention Description and Replication (TIDieR) reporting guideline was developed to improve the reporting of interventions in RCT protocols and results papers. Reporting completeness in protocols of diet or nutrition-related RCTs has not been systematically investigated. We aim to identify published protocols of diet or nutrition-related RCTs, assess their reporting completeness and identify the main reporting limitations remaining in this field. METHODS AND ANALYSIS: We will conduct a meta-research study of RCT protocols published in journals indexed in at least one of six selected databases between 2012 and 2022. We have run a search in PubMed, Embase, CINAHL, Web of Science, PsycINFO and Global Health using a search strategy designed to identify protocols of diet or nutrition-related RCTs. Two reviewers will independently screen the titles and abstracts of records yielded by the search in Rayyan. The full texts will then be read to confirm protocol eligibility. We will collect general study features (publication information, types of participants, interventions, comparators, outcomes and study design) of all eligible published protocols in this contemporary sample. We will assess reporting completeness in a randomly selected sample of them and identify their main reporting limitations. We will compare this subsample with the items in the SPIRIT and TIDieR statements. For all data collection, we will use data extraction forms in REDCap. This protocol is registered on the Open Science Framework (DOI: 10.17605/OSF.IO/YWEVS). ETHICS AND DISSEMINATION: This study will undertake a secondary analysis of published data and does not require ethical approval. The results will be disseminated through journals and conferences targeting stakeholders involved in nutrition research