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  1. Laser powder bed fusion (L-PBF) additive manufacturing has been used to fabricate complex-shaped structures, which often consist of fine features. Due to transient process phenomena, there are differences in terms of the melt pool formation and the surface morphology depending upon the feature area and scan parameters. This study investigates the scan length effect on the surface morphology and the presence of transient length and width that may have a significant effect as the layer addition continues. For this purpose, four scan lengths (0.25 mm, 0.5 mm, 1.0 mm, and 2.0 mm) are used to fabricate six tracks with back-and-forth scanning. A full factorial design of experiments is used to form multi-track depositions with three levels of power (125 W, 160 W, and 195 W), two levels of scan speed (550 mm/s and 1000 mm/s), and four levels of hatch spacing (80 μm, 100 μm, 120 μm, and 140 μm). A white light interferometer is used to acquire the surface data, and MATLAB is used for surface topographical analysis. The results indicated that the scan length has a significant effect on the surface characteristics. The average height of multi-track deposits increases with the decrease of the scan length. Moreover, themore »transient length and width can be approximated based on the height variation along both the scan and transverse directions, respectively.« less
    Free, publicly-accessible full text available June 27, 2023
  2. Free, publicly-accessible full text available March 1, 2023
  3. In this study, different hatch spacings were used to fabricate single layer and multiple layers, and its effect on porosity was investigated by using microcomputed tomography. The combination of laser power (100 W, 150 W, 175 W, and 195W) and scan speeds (600 mm/s, 800 mm/s, 1000 mm/s and 1200 mm/s) which resulted in the least number of pores were selected from the previous single-track experiment. Six levels of hatch spacings were selected based on the track width to form single and multiple layers: 60%, 70%, 80%, 90%, 120% and 150% of track widths. For the multilayer build, the variation in keyhole porosity within the given window of parameters were found to be attributed to the variation in the hatch spacing. In general, the pore number decreased with increase in hatch spacing from 60% to 90% but increased when hatch spacing further increased from 90% to 120%.
  4. Transplantation of human embryonic stem cell (hESC)-derived neural progenitors is a potential treatment for neurological disorders, but relatively little is known about the time course for human neuron maturation after transplantation and the emergence of morphological and electrophysiological properties. To address this gap, we transplanted hESC-derived human GABAergic interneuron progenitors into the mouse hippocampus, and then characterized their electrophysiological properties and dendritic arborizations after transplantation by means of ex vivo whole-cell patch clamp recording, followed by biocytin staining, confocal imaging and neuron reconstruction software. We asked whether particular electrophysiological and morphological properties showed maturation-dependent changes after transplantation. We also investigated whether the emergence of particular electrophysiological properties were linked to increased complexity of the dendritic arbors. Human neurons were classified into five distinct neuronal types (Type I-V), ranging from immature to mature fastspiking interneurons. Hierarchical clustering of the dendritic morphology and Sholl analyses suggested four morphologically distinct classes (Class A-D), ranging from simple/immature to highly complex. Incorporating all of our data regardless of neuronal classification, we investigated whether any electrophysiological and morphological features correlated with time post-transplantation. This analysis demonstrated that both dendritic arbors and electrophysiological properties matured after transplantation.
  5. GABAergic interneuron dysfunction has been implicated in temporal lobe epilepsy (TLE), autism, and schizophrenia. Inhibitory interneuron progenitors transplanted into the hippocampus of rodents with TLE provide varying degrees of seizure suppression. We investigated whether human embryonic stem cell (hESC)-derived interneuron progenitors (hESNPs) could differentiate, correct hippocampal-dependent spatial memory deficits, and suppress seizures in a pilocarpine-induced TLE mouse model. We found that transplanted ventralized hESNPs differentiated into mature GABAergic interneurons and became electrophysiologically active with mature firing patterns. Some mice developed hESNP-derived tumor-like NSC clusters. Mice with transplants showed significant improvement in the Morris water maze test, but transplants did not suppress seizures. The limited effects of the human GABAergic interneuron progenitor grafts may be due to cell type heterogeneity within the transplants.
  6. Abstract The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.
    Free, publicly-accessible full text available December 1, 2023
  7. Abstract The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with Geant4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation—the calorimeter shower simulation—with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges, and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes.
    Free, publicly-accessible full text available December 1, 2023