Capturing Marangoni flow via synchrotron imaging of selective laser melting

Marangoni flow has a substantial influence on the quality of components fabricated via laser powder bed fusion (LPBF). However, Marangoni flow in melt pools is rarely quantified due to the opacity of liquid metals and the necessity for in situ evaluation. Here we report the findings of high-temporal-resolution synchrotron x-ray radiography experiments tracking the flow in the melt-pool. Dense, highly attenuating tungsten carbide particles are seeded within an elemental powder blend of aluminium and copper of varying composition. Due to the extremely high temporal resolution of greater than 50 kfps at the 31-ID-B beamline at the Advanced Photon Source, USA, we can track the position of tracer particles from frame to frame. This data provides valuable process guidance for optimising mixing and informs the development and validation of multiphysics models

Modelling the complex evaporated gas flow and its impact on particle spattering during laser powder bed fusion

The additive manufacturing (AM) of metals is becoming an increasingly important production process with the potential to replace traditional techniques such as casting. Laser Powder Bed Fusion (LPBF) is used in many applications to print metal parts from powder. The metal powder is heated locally with sufficient laser radiation that the liquid melt easily reaches its boiling temperature, which leads to a metallic vapour jet that can entrain both powder bed particles and molten droplets. The small size of laser-matter interaction site makes a detailed experimental analysis of the process challenging. Synchrotron X-ray imaging experiments are one of the few methods which can capture the dynamic melting and solidification processes. Comparing such experiments with computer simulations of the process is an important approach in order to better understand the manufacturing process and to analyse the influence of process parameters on the evaporated gas jet and the subsequent impact on particle ejection, leading to potentially reduced AM component quality. The melting and solidification of the metal powder is simulated using an Eulerian multiphase approach based on a control volume discretization of powder bed and substrate and a volume of liquid separation from melt and gas phase. The gas phase modelled as an ideal gas reaches velocities up to 100 m/s. Lagrangian particle tracking in the simulation demonstrates that the velocity fields calculated by the Eulerian multi-phase approach in combination with a standard drag-force model lead to particle accelerations in good agreement with those measured experimentally. In order to avoid numerical laborious Lagrangian calculations, a direct method to compare an Eulerian multiphase simulation with synchrotron X-ray experiments was introduced and validated. This approach is used to analyse the influence of process parameters including laser power and laser speed on the maximal acceleration of particles from the melt pool area. While the particle acceleration increases linearly with line energy in the conduction mode, a linear decrease of the acceleration with increasing line energy can be found in the transition mode before the acceleration increases again with line energy in the keyhole mode

Two cases of food aversion with semantic dementia

Accounts of altered eating behavior in semantic dementia generally emphasize gluttony and abnormal food preferences. Here we describe two female patients with no past history of eating disorders who developed early prominent aversion to food in the context of an otherwise typical semantic dementia syndrome. One patient (aged 57) presented features in line with anorexia nervosa while the second patient (aged 58) presented with a syndrome more suggestive of bulimia nervosa. These cases add to the growing spectrum of apparently dichotomous behavior patterns in the frontotemporal dementias and illustrate a potentially under-recognized cause of eating disorders presenting in later life

Synchrotron validation of inline coherent imaging for tracking laser keyhole depth

In situ monitoring is critical to the increasing adoption of laser powder bed fusion (LPBF) and laser welding by industry for manufacture of complex metallic components. Optical coherence tomography (OCT), an interferometric imaging technique adapted from medical applications, is now widely used for operando monitoring of morphology during high-power laser material processing. However, even in stable processing regimes, some OCT depth measurements from the keyhole (vapor cavity formed at laser beam spot) appear too shallow or too deep when compared to ex situ measurements of weld depth. It has remained unclear whether these outliers are due to imaging artifacts, multiple scattering of the imaging beam within the keyhole, or real changes in keyhole depth, making it difficult to accurately extract weld depth and determine error bounds. To provide a definitive explanation, we combine inline coherent imaging (ICI), a type of OCT, with synchrotron X-ray imaging for simultaneous, operando monitoring of the full 2-dimensional keyhole profile at high-speed (280 kHz and 140 kHz, respectively). Even in a highly turbulent pore-generation mode, the depth measured with ICI closely follows the keyhole depth extracted from radiography (>80% within ± 14 µm). Ray-tracing simulations are used to confirm that the outliers in ICI depth measurements (that significantly disagree with radiography) primarily result from multiple reflections of the imaging light (57%). Synchrotron X-ray imaging also enables tracking of bubble and pore formation events. Pores are generated during laser welding when the sidewalls of the keyhole rapidly (>10 m/s) collapse inwards, pinching off a bubble from the keyhole root and resulting in a rapid decrease in keyhole depth. Evidence of bubble formation can be found in ICI depth profiles alone, as rapid depth changes exhibit moderate correlation with bubble formation events (0.26). This work moves closer to accurate, localized defect detection during laser welding and LPBF using ICI

The effect of dynamical scattering on single-plane phase retrieval in electron ptychography

Segmented and pixelated detectors on scanning transmission electron microscopes enable the complex specimen transmission function to be reconstructed. Imaging the transmission function is key to interpreting the electric and magnetic properties of the specimen, and as such four-dimensional scanning transmission electron microscopy (4D-STEM) imaging techniques are crucial for our understanding of functional materials. Many of the algorithms used in the reconstruction of the transmission function rely on the multiplicative approximation and the (weak) phase object approximation, which are not valid for many materials, particularly at high resolution. Herein, we study the breakdown of simple phase imaging in thicker samples. We demonstrate the behavior of integrated center of mass imaging, single-side band ptychography, and Wigner distribution deconvolution over a thickness series of simulated GaN 4D-STEM datasets. We further give guidance as to the optimal focal conditions for obtaining a more interpretable dataset using these algorithms

Discourse stylistics and detective fiction:A case study

Pedagogical stylistics concerns itself with the practice of teaching stylistics in the classroom. The principal aim of such teaching is to make students aware of language use in the texts chosen for study. What characterizes pedagogical stylistics is that classroom activities are interactive between the text and the (student) reader, with both the texts and the activities usually chosen by the teacher (see Clark 1996; Clark and Zyngier 2003; Clark and McRae 2004; Simpson 2004). Part of this self-same process of improving students’ linguistic sensibilities has to include placing greater emphasis upon the text as action: the mental processing which is such a proactive part of reading and interpretation, and how all these elements – pragmatic and cognitive as well as linguistic – function within quite specific social and cultural contexts

In situ synchrotron investigation of degenerate graphite nodule evolution in ductile cast iron

Ductile cast irons (DCIs) are of increasing importance in the renewable energy and transportation sectors. The distribution and morphology of the graphite nodules, in particular the formation of degenerate features during solidification, dictate the mechanical performance of DCIs. In situ high-speed synchrotron X-ray tomography was used to capture the evolution of graphite nodules during solidification of DCI, including degenerate features and the effect of the carbon concentration field. The degeneration of nodules is observed to increase with re-melting cycles, which is attributed to Mg-loss. The dendritic primary austenite and carbon concentration gradients in the surrounding liquid phase were found to control nodule morphology by locally restricting and promoting growth. A coupled diffusion-mechanical model was developed, confirming the experimentally informed hypothesis that protrusions form through liquation cracking of the austenite shell and subsequent localised growth. These results provide valuable insights into the solidification kinetics of cast irons, supporting the design of advanced alloys

Physiological phenotyping of dementias using emotional sounds.

INTRODUCTION: Emotional behavioral disturbances are hallmarks of many dementias but their pathophysiology is poorly understood. Here we addressed this issue using the paradigm of emotionally salient sounds. METHODS: Pupil responses and affective valence ratings for nonverbal sounds of varying emotional salience were assessed in patients with behavioral variant frontotemporal dementia (bvFTD) (n = 14), semantic dementia (SD) (n = 10), progressive nonfluent aphasia (PNFA) (n = 12), and AD (n = 10) versus healthy age-matched individuals (n = 26). RESULTS: Referenced to healthy individuals, overall autonomic reactivity to sound was normal in Alzheimer's disease (AD) but reduced in other syndromes. Patients with bvFTD, SD, and AD showed altered coupling between pupillary and affective behavioral responses to emotionally salient sounds. DISCUSSION: Emotional sounds are a useful model system for analyzing how dementias affect the processing of salient environmental signals, with implications for defining pathophysiological mechanisms and novel biomarker development

The effect of mixing entire male pigs prior to transport to slaughter on behaviour, welfare and carcass lesions

peer-reviewedData set for article is also provided.Research is needed to validate lesions recorded at meat inspection as indicators of pig welfare on farm. The aims were to determine the influence of mixing pigs on carcass lesions and to establish whether such lesions correlate with pig behaviour and lesions scored on farm. Aggressive and mounting behaviour of pigs in three single sex pens was recorded on Day −5, −2, and −1 relative to slaughter (Day 0). On Day 0 pigs were randomly allocated to 3 treatments (n = 20/group) over 5 replicates: males mixed with females (MF), males mixed with males (MM), and males unmixed (MUM). Aggressive and mounting behaviours were recorded on Day 0 at holding on farm and lairage. Skin/tail lesions were scored according to severity at the farm (Day −1), lairage, and on the carcass (Day 0). Effect of treatment and time on behaviour and lesions were analysed by mixed models. Spearman rank correlations between behaviour and lesion scores and between scores recorded at different stages were determined. In general, MM performed more aggressive behaviour (50.4 ± 10.72) than MUM (20.3 ± 9.55, P < 0.05) and more mounting (30.9 ± 9.99) than MF (11.4 ± 3.76) and MUM (9.8 ± 3.74, P < 0.05). Skin lesion scores increased between farm (Day −1) and lairage (P < 0.001), but this tended to be significant only for MF and MM (P = 0.08). There was no effect of treatment on carcass lesions and no associations were found with fighting/mounting. Mixing entire males prior to slaughter stimulated mounting and aggressive behaviour but did not influence carcass lesion scores. Carcass skin/tail lesions scores were correlated with scores recorded on farm (rskin = 0.21 and rtail = 0.18, P < 0.01) suggesting that information recorded at meat inspection could be used as indicators of pig welfare on farm.This study was part of the PIGWELFIND project funded by the Department of Agriculture, Food and the Marine (DAFM), Ireland