Dixon University Center

Solid particle erosion occurs when small high speed particles impact surfaces. It can be either destructive such as in the erosion of oil pipelines by corrosion byproducts, or constructive such as in abrasive jet machining processes. Two dimensional finite element (FE) models of single rhomboid particles impact on a copper target were developed using two different techniques to deal with the problem of element distortion: (i) element deletion, and (ii) remeshing. It was found that the chip formation and the material pile-up, two phenomena that cannot be simulated using a previously developed rigid-plastic model, could be simulated using the FE models, resulting in a good agreement with experiments performed using a gas gun. However, remeshing in conjunction with a failure model caused numerical instabilities. The element deletion approach also induced errors in mass loss due to the removal of distorted elements. To address the limitations of the FE approach, smoothed particle hydrodynamics (SPH) which can better accommodate large deformations, was used in the simulation of the impact of single rhomboid particles on an aluminum alloy target. With appropriate constitutive and failure parameters, SPH was demonstrated to be suitable for simulating all of the relevant damage phenomena observed during impact experiments. A new methodology was developed for generating realistic three dimensional particle geometries based on measurements of the size and shape parameter distributions for a sample of 150 µm nominal diameter angular aluminum oxide powder. The FE models of these generated particles were implemented in a SPH/FE model to simulate non-overlapping particle impacts. It was shown that the simulated particles produced distributions of crater and crater lip dimensions that agreed well with those measured from particle blasting experiments. Finally, a numerical model for simulating overlapping impacts of angular particles was developed and compared to experimental multi-particle erosion tests, with good agreement. An investigation of the simulated trajectory of the impacting particles revealed various erosion mechanisms such as the micromachining of chips, the ploughing of craters, and the formation, forging and knocking off crater lips which were consistent with previously noted ductile solid particle erosion mechanisms in the literature.

Introduction: Neurologic deterioration (ND) occurs in a quarter of acute lacunar infarcts and may lead to severe disability, but underlying pathophysiology of ND remains poorly understood. We sought to identify risk factors and clinical characteristics associated with ND. Methods: This retrospective observational study included consecutive patients with acute lacunar stroke admitted to New York University Langone Health and Brown University (NYU/Brown). Lacunar stroke was defined as a subcortical infarct <1.5 cm on CT or <2 cm on diffusion-weighted imaging without significant stenosis (>50%) in the parent vessel and no cardioembolic source. We defined ND as any neurologic deterioration referable to the lacunar stroke and not related to a medical or non-cerebrovascular neurological complication. We used logistic regression analyses to determine associations between ND and luminal stenosis (<50%) vs no luminal stenosis, after adjustment for key confounders. Furthermore, we attempted to validate findings using the Columbia University (CU) stroke registry and perform a meta-analysis combining the derivation and validation groups due to expected small samples and event rates. Results: The NYU/Brown sample included 205 patients, of whom 41 (20%) had ND. In adjusted models, we found no definite association between luminal stenosis and ND (aOR 1.74, 95% CI 0.73-4.14). From CU, 361 total patients were included, of whom 59 (16%) had ND. In adjusted models, we found an association between luminal stenosis and ND (aOR 2.28 95% CI 1.15-4.50). Meta-analysis of both cohorts found luminal stenosis associated with ND (RR [95% CI]: 1.75 [1.23-2.49]). Conclusions: In this multi-center study, luminal stenosis (<50%) may be associated with ND following an acute lacunar infarct. Larger studies using high-resolution vascular imaging modalities such as vessel wall imaging are needed to validate our findings.

Birds that migrate across high altitude mountain ranges are faced with the challenge of maintaining vigorous exercise in environments with limited oxygen. Ruddy shelducks are known to use wintering grounds south of the Tibetan Plateau at sea level and breeding grounds north of Himalayan mountain range. Therefore, it is likely these shelducks are preforming high altitude migrations. In this study we analyse satellite telemetry data collected from 15 ruddy shelduck from two populations wintering south of the Tibetan Plateau from 2007 to 2011. During north and south migrations ruddy shelduck travelled 1481 km (range 548–2671 km) and 1238 km (range 548–2689 km) respectively. We find mean maximum altitudes of birds in flight reached 5590 m (range of means 4755–6800 m) and mean maximum climb rates of 0.45 m s–1 (range 0.23–0.74 m s–1). The ruddy shelduck is therefore an extreme high altitude migrant that has likely evolved a range of physiological adaptations in order to complete their migrations.

Over the course of one high school basketball season, a coach chronicled his journey as a mentor of his captains, leadership development and conducted a self-study on the data. Through field notes, interviews with captains, and journals, the coach described his successes and failures as a mentor in allowing captains to use their personal voice, distributing and delegating leadership tasks to captains, offering reminders of important leadership concepts, learning to mentor athletically skilled but quiet or inconsistent captains, and setting an effective example as the coach. Following the data presentation, a discussion regarding future research opportunities and practical applications for coaches is provided.

Frequency: Yearly ISSN: 0015-198X eISSN: 1938-3312 https://www.tandfonline.com/doi/abs/10.1080/0015198X.2021.1965861 Abstract Assets whose carry is trending up, namely, assets with high carry momentum, tend to have higher returns than those with low carry momentum. Using data from different asset classes, we show that portfolios with high-carry-momentum assets delivered higher returns than portfolios with low-carry-momentum assets. The return differentials cannot be explained by exposure to traditional market risks or by such seemingly related factors as time-series momentum and carry. The results can be motivated by a model in which investors’ demand for an asset depends on the market’s view on the expected returns. An increase in carry raises investors’ belief in the attractiveness of an asset, leading to the possibility for higher demand in the market and in turn to the potential for higher prices and positive returns.

Current dosimetric protocols based on the absorbed dose (AAPM TG-51 and IAEA TRS-398 protocols) require calibration measurements under reference conditions. For some radiotherapy systems, this requirement cannot be met, and calibration has to be performed under nonreference experimental conditions. In order to solve this problem, both protocols can be extended by inclusion of the measured-to-reference conversion factor, k(mr). In order to determine this factor, basic dosimetric quantities, like stopping power ratios, mass attenuation coefficients and chamber correction factors have to be calculated. If measurements are not feasible, accurate Monte Carlo modeling is required. The extension of the protocols is illustrated using the case of the helical tomotherapy radiation unit, where the typical calibration measurement conditions are the 10 x 5 cm2 field size and the 85 cm surface source distance, limited by the system design. It was calculated that the k(mr) factor for this conditions is close to unity (0.997+/-0.001). In addition, the deviation of the measurement conditions from the reference conditions results in the change of the quality conversion factor (approximately 0.995-0.998, depending on the ionization chamber used). This change is the same regardless of the used calibration protocol. For smaller field sizes the corrections become more significant, resulting in the total correction factor compared to the reference conditions of up to 1.5% for the smallest considered field size of 2 x 2 cm2.