•UAV-SfM soil loss measurements were validated by direct sediment collection.•Photogrammetric precision estimates defined spatially variable levels of detection.•DEMs of difference illustrated the ...diffuse erosion patterns through time.•Accurate 3-D soil surface models were constructed from UAV-SfM data.
Sheet erosion is common on agricultural lands, and understanding the dynamics of the erosive process as well as the quantification of soil loss is important for both soil scientists and managers. However, measuring rates of soil loss from sheet erosion has proved difficult due to requiring the detection of relatively small surface changes over extended areas. Consequently, such measurements have relied on the use of erosion plots, which have limited spatial coverage and have high operating costs. For measuring the larger erosion rates characteristic of rill and gully erosion, structure-from-motion (SfM) photogrammetry has been demonstrated to be a valuable tool. Here, we demonstrate the first direct validation of UAV-SfM measurements of sheet erosion using sediment collection data collected from erosion plots.
Three erosion plots (12 m × 4 m) located at Lavras, Brazil, with bare soil exposed to natural rainfall from which event sediment and runoff was monitored, were mapped during two hydrological years (2016 and 2017), using a UAV equipped with a RGB camera. DEMs of difference (DoD) were calculated to detect spatial changes in the soil surface topography over time and to quantify the volumes of sediments lost or gained. Precision maps were generated to enable precision estimates for both DEMs to be propagated into the DoD as spatially variable vertical uncertainties.
The point clouds generated from SfM gave mean errors of ~2.4 mm horizontally (xy) and ~1.9 mm vertically (z) on control and independent check points, and the level of detection (LoD) along the plots ranged from 1.4 mm to 7.4 mm. The soil loss values obtained by SfM were significantly (p < 0.001) correlated (r2 = 95.55%) with those derived from the sediment collection. These results open up the possibility to use SfM for erosion studies where channelized erosion is not the principal mechanism, offering a cost-effective method for gaining new insights into sheet, and interrill, erosion processes.
Lava rheology and effusion rate are critical factors in determining the evolution of lava flows. However, direct and accurate field measurements are difficult to carry out, and estimates are usually ...based on measurements of the flow’s surface velocity and assumptions of sub-surface geometry. Using numerical flow models, we show that the potential for error due to geometry uncertainty is minimized if a semi-elliptical cross-sectional channel shape is assumed. Flow is simulated for isothermal Newtonian, temperature-dependent Newtonian, and isothermal power-law rheology lavas. For isothermal Newtonian lava, we find that the error in channel shape alone can make apparent viscosity estimates ∼3.5 times too large (e.g., for inappropriate use of the Jeffreys equation on a narrow semi-elliptical channel). For a temperature-dependent rheology, using an analytical approximation for Newtonian flow in a semi-elliptical geometry yields apparent viscosity and flux values that are more accurate than estimates which assume a rectangular geometry, for all channel shapes considered, including rectangular channels. Viscosity calculations for real channels on Mauna Loa and Mount Etna show that for a Newtonian rheology, a semi-elliptical analytical solution gives an approximation three times closer to the actual viscosity than a rectangle with the same depth while, if the lava is shear-thinning (power law exponent
m
= 0.6), a rectangular approximation is 15 % more accurate. Our results can be used to bracket possible viscosity and flux estimates when channel topography is poorly constrained.
During effusive eruptions, thermal satellite monitoring has proved well suited to map the thermal flux from lava flows. However, during lava fountaining events, thermal contributions from active ...flows and from the fountain itself cannot be separated in low resolution satellite data. Here using photogrammetry and atmospheric modeling techniques, we compare radiance estimates from long‐range ground‐based thermal camera data (from which the fountain can be excluded) with those from SEVIRI satellite images for a fountaining event at Mount Etna (12 August 2011). The radiant heat flux determined from the ground‐based camera showed similar behavior to values retrieved from Spinning Enhanced Visible and Infrared Imager (SEVIRI); thus the SEVIRI signal is interpreted to be dominated by the lava flows, with minimal contribution from the fountain. Furthermore, by modeling the cooling phase of each pixel inundated by lava, the mean thickness and lava volume (~2.4 × 106 m3) derived from camera images are comparable with those calculated from SEVIRI (~2.8 × 106 m3).
Key Points
A new technique to analyze long‐range ground‐based thermal images is developed
Heat flux and lava volume derived from camera and SEVIRI data are comparable
SEVIRI data are more sensitive to lava flows than to simultaneous fountaining
Prosthetic joint infection (PJI) is a devastating complication. Studies have suggested reduction in PJI with the use of ceramic bearings.
Adult patients who underwent total hip arthroplasty (THA) ...using an uncemented acetabular component with ceramic-on-ceramic (CoC), ceramic-on-polyethylene (CoP), or metal-on-polyethylene (MoP) bearing surfaces between 2002 and 2016 were extracted from the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man. A competing risk regression model to investigate predictors of each revision outcome was used. Time-to-event was determined by duration of implantation since primary surgery with competing risks being death or revision. The results were adjusted for age, gender, American Association of Anaesthesiologists grade, body mass index, surgical indication, intraoperative complications, and implant data.
In total, 456,457 THAs (228,786 MoP, 128,403 CoC, and 99,268 CoP) were identified. Multivariable modeling showed that the risk of revision for PJI was significantly lower with CoC (risk ratio 0.748, P < .001) and CoP (risk ratio 0.775, P < .001) compared to MoP. Significant reduction in risk of aseptic and all-cause revision was also seen. The significant protective effect of ceramic bearing was predominantly seen 2 years after implantation. Aseptic revision beyond 2 years reduced by 18.1% and 24.8% for CoC and CoP (P < .001), respectively. All-cause revision rate beyond 2 years reduced by 21.6% for CoC and 27.1% for CoP (P < .001)
This study demonstrates an association between the use of ceramic as part of the bearing, with lower rates of revision for all causes, revision for infection, and revision for aseptic causes, supporting ceramic bearings in THA.
The current (March 2008 to February 2009) summit eruptive activity at Kilauea Volcano is characterized by explosive degassing bursts accompanied by very long period (VLP) seismic signals. We model ...the source mechanisms of VLP signals in the 10–50 s band using data recorded for 15 bursts with a 10‐station broadband network deployed in the summit caldera. To determine the source centroid location and source mechanism, we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account. The VLP signals associated with the bursts originate in a source region ∼1 km below the eastern perimeter of Halemaumau pit crater. The observed waveforms are well explained by the combination of a volumetric component and a vertical single force component. For the volumetric component, several source geometries are obtained which equally explain the observed waveforms. These geometries include (1) a pipe dipping 64° to the northeast; (2) two intersecting cracks including an east striking crack (dike) dipping 80° to the north, intersecting a north striking crack (another dike) dipping 65° to the east; (3) a pipe dipping 58° to the northeast, intersecting a crack dipping 48° to the west–southwest; and (4) a pipe dipping 57° to the northeast, intersecting a pipe dipping 58° to the west–southwest. Using the dual‐crack model as reference, the largest volume change obtained among the 15 bursts is ∼24,400 m3, and the maximum amplitude (peak to peak) of the force is ∼20 GN. Each burst is marked by a similar sequence of deflation and inflation, trailed by decaying oscillations of the volumetric source. The vertical force is initially upward, synchronous with source deflation, then downward, synchronous with source reinflation, followed by oscillations with polarity opposite to the volumetric oscillations. This combination of force and volume change is attributed to pressure and momentum changes induced during a fluid dynamic source mechanism involving the ascent, expansion, and burst of a large slug of gas within the upper ∼150 m of the magma conduit. As the slug expands upon approach to the surface and more liquid becomes wall supported by viscous shear forces, the pressure below the slug decreases, inducing conduit deflation and an upward force on the Earth. The final rapid slug expansion and burst stimulate VLP and LP oscillations of the conduit system, which slowly decay due to viscous dissipation and elastic radiation. Consideration of the fluid dynamic arguments leads us to prefer the dual‐crack VLP source model as it is the only candidate model capable of producing plausible values of length scales and pressure changes. The magnitudes of the vertical forces observed in the 15 bursts appear consistent with slug masses of 104 to 106 kg.
BACKGROUND:There is evidence to support the use of highly cross-linked polyethylene (HXLPE) in patients undergoing total hip arthroplasty. However, the benefits for those undergoing total knee ...arthroplasty are uncertain, with conflicting reports based on previous cohort analyses. The purpose of the present study was to compare the revision rates following primary total knee arthroplasty with use of HXLPE as compared with conventional polyethylene (CPE) using data from the National Joint Registry (NJR) for England, Wales and Northern Ireland.
METHODS:We performed a retrospective analysis of primary total knee arthroplasties recorded in the NJR from 2003 to 2014. Cobalt-chromium (CoCr)-CPE and CoCr-HXLPE bearing surfaces were compared using all-cause revision, aseptic revision, and septic revision as end points. Survival analyses were conducted using rates per 100 years observed, Kaplan-Meier survival estimates, and Cox regression hazard ratios (HRs) adjusted for age, sex, American Society of Anesthesiologists (ASA) classification, body mass index (BMI), lead surgeon grade, and implant constraint. Secondary analyses compared the most commonly used HXLPEs (Zimmer Prolong, DePuy XLK, and Stryker X3) against CPE for the 3 most common total knee arthroplasty systems (NexGen, PFC Sigma, and Triathlon).
RESULTS:In the present study of 550,658 total knee arthroplasties, the unadjusted aseptic revision rates were significantly lower following procedures performed with CPE (n = 513,744) as compared with those performed with HXLPE total knee replacements (n = 36,914) (0.29 95% confidence interval (CI), 0.28 to 0.30 compared to 0.38 95% CI, 0.35 to 0.42, p < 0.01). The 10-year HR associated with CPE was 0.4 (95% CI, 0.1 to 0.8, p = 0.03). There were no significant differences between the adjusted revision rates of HXPLE compared with CPE in individual analyses of the most common total knee arthroplasty systems. However, for the subset of patients who were both <60 years of age and had a BMI of >35 kg/m, the “second-generation” Stryker X3 HXLPE demonstrated significantly better survival than its respective CPE, with CPE having an HR of 2.6 (95% CI, 1.2 to 5.9) (p = 0.02).
CONCLUSIONS:Alternative bearings are marketed as having improved wear properties over traditional CoCr-CPE. This registry-based analysis demonstrated no overall survival benefit of HXLPE after a maximum duration of follow-up of 12 years. Because of their increased cost, the routine use of HXLPE bearings may not be justified. However, they may have a role in specific “higher demand” groups such as patients <60 years of age and/or those with a BMI of >35 kg/m.
LEVEL OF EVIDENCE:Therapeutic Level III. See Instructions for Authors for a complete list of levels of evidence.
The Murray–Darling Basin in south‐eastern Australia contains over 70,000 km2 of wetlands and floodplains, many of which are in poor condition. In response, Australian governments have committed to a ...major restoration program, the Murray–Darling Basin Plan that includes management of 2,750 Gl of environmental water to protect and restore aquatic ecosystems. The restoration is being undertaken within an adaptive management framework that includes monitoring the outcomes of environmental flows in seven river valleys. This paper provides an overview of the 5‐year monitoring project and some preliminary results. Monitoring design considered the Basin Plan's environmental objectives, conceptual models of ecosystem responses to flow, and an outcomes framework linking flow responses to the environmental objectives. Monitoring indicators includes ecosystem type, vegetation, river metabolism, and fish. Responses are evaluated to identify the contribution of environmental flows to Basin Plan environmental objectives and continual improvements in management. The program is unique in that it seeks to monitor long‐term outcomes of environmental flows at the river basin scale. Despite many challenges, the monitoring has become a key part of the adaptive management of environmental flows in the Murray–Darling Basin.
Recent research has revealed that low volume resistance ‘priming’ exercise may improve neuromuscular performance when completed within 48h before competition. The aim of this study was to investigate ...the current prevalence and application of this strategy by practitioners in sport.
This study surveyed practitioners who were currently programming and/or prescribing resistance training programs for high performance athletes.
Sixty-nine practitioners completed the online survey relating to their perceptions of resistance priming exercise strategies and the training methods prescribed in the days prior to competition.
Fifty-one percent of respondents currently prescribed priming exercise. Of the practitioners who prescribed this strategy, most respondents (59%) prescribed this session within 8h of competition. Sessions typically included 2–3 upper body and lower body exercises (mean=2.5±0.7 and 2.1±0.6 respectively), usually involving both loaded and unloaded activities. Large variations in exercise selection were reported, however, unloaded jumps (87%), loaded jumps (60%) and bench press (56%) were commonly prescribed. A low volume of sets (mean=2.8±0.9) and repetitions (mean=3.8±1.3) were used during these sessions. Lastly, various resistance loading strategies were prescribed, ranging from unloaded activities to heavy loaded exercises performed at ≥85% 1RM.
Priming exercise is currently prescribed by many practitioners to prepare athletes for competition. A wide range of priming exercise methods are used, despite limited evidence supporting these methods. Future research should examine the effects of the various priming methods which are currently applied in practice.
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