1,746 research outputs found
Influence of power source dynamics on metal and heat transfer behaviors in pulsed gas metal arc welding
No full textA numerical model has been constructed based on the solution of the magnetohydrodynamic equations within the framework of phase field algorithm to simulate the metal transfer process and to investigate the effect of power source dynamics on metal transfer and heat transfer behaviors in pulsed gas metal arc welding. Three typical kinds of power source dynamics (i.e. exponential, ideal square and trapezoidal waveform) using identical nominal pulsing parameters are considered and compared. The ideal square waveform with infinitely steep-sided pulse would lead to a higher detaching speed and an earlier detachment than other waveforms. Decrease in the response rate of the power source shows a retarding effect on the dynamic characteristics of the metal transfer, leading to a delay of detachment and a lower detaching speed. Moreover, this retarding effect is more and more significant as the response rate decreased and may even alter the transfer mode from one-drop-per-pulse to an undesired irregular pattern. Besides, a quantitative analysis of the heat fluxes into the electrode is further conducted, and the result shows that power source dynamics only has a quite slight influence on the heat transfer behavior. (C) 2018 Elsevier Ltd. All rights reserved.
Characterization of Ductile Crack Propagation by Fractal Energy Dissipation Rate
No full textBecause of its geometry dependence and loss of physical meaning, the incremental crack resistance curve cannot characterize ductile fractures with large crack extensions and plastic deformations. Therefore, the energy dissipation rate R is employed to overcome these deficiencies, even though specimen size effects still exist. In the study, considering the fractal crack path and concomitant plastic dissipation in the fractal domain, a scale-invariant energy dissipation rate, γp*, is proposed in the context of renormalization group theory. Some experiments in the literature have validated this approach. The fitted fractal energy dissipation rate is independent of the specimen size and initial crack length; moreover, as the specimen size increases, progressive fractality vanishing is found consistently with geometrical multifractality
Effect of pulsing parameters on drop transfer dynamics and heat transfer behavior in pulsed gas metal arc welding
No full textThe effect of pulsing parameters on the metal and heat transfer behaviors in pulsed gas metal arc welding is investigated by a numerical model based on the solution of the magnetohydrodynamic equations within the framework of phase field method. Five sets of current waveforms using different peak current and duration (i.e. 300 A-2.30 ms, 350 A-1.80 ms, 400 A-1.45 ms, 450 A-1.20 ms and 500 A-1.00 ms) but maintaining an identical average current (i.e. 170 A) are considered and compared. The pulses using higher current but shorter duration result in more elongated shape of the pendent drop, earlier detachment, and significantly higher velocity of the detached drop. Unlike the drop velocity, higher peak current merely leads to a slight increase in the average temperature of the detached drop. The reason for this slight increase is that only the joule heating increases with the peak current, while the sheath heating and arc heating is governed by the average current and keeps almost constant using different pulsing parameters. The simulation results are compared with the high speed photos and exhibit good agreements. (C) 2018 Elsevier Ltd. All rights reserved.
sj-docx-1-jaf-10.1177_0148558X221100864 – Supplemental material for Customer Concentration and Managerial Bad News Withholding
No full textSupplemental material, sj-docx-1-jaf-10.1177_0148558X221100864 for Customer Concentration and Managerial Bad News Withholding by Yangyang Chen, Gang Hu, Jun Yao and Jingran Zhao in Journal of Accounting, Auditing & Finance</p
CCDC 1905707: Experimental Crystal Structure Determination
No full textRelated Article: Ximei Zhao, Bing Tian, Yangyang Yang, Xiaojia Si, Florian F. Mulks, Matthias Rudolph, Frank Rominger, A. Stephen K. Hashmi|2019|Adv.Synth.Catal.|361|3155|doi:10.1002/adsc.20190026
Interleukin-1 mediated cell-type specific signaling in hippocampal neurons and astrocytes
No full textInterleukin-1β (IL-1β) is a pro-inflammatory cytokine that is implicated in immune and inflammatory responses. In the central nervous system (CNS), IL-1β is synthesized and released during injury, infection, and many neurodegenerative diseases, but also under physiological conditions. Several IL-1-mediated signaling pathways and effects have been identified in hippocampal neurons and astrocytes, but their mechanisms have not been fully defined. IL-1 signaling requires the type one IL-1 receptor (IL-1RI) as well as IL-1 receptor accessory protein (IL-1RAcP) as a receptor partner. A novel isoform of the IL-1 receptor accessory protein, AcPb, has also been found in the CNS, but its role remains unclear. This thesis examined AcPb function in regulating IL-1β signaling. The results showed that IL-1β activated p38 MAPK but not NFκB in neurons. In astrocytes, IL-1β induced both p38 and NFκB pathways in regulating inflammatory responses. AcPb was not involved in mediating either p38 or NFκB in either cell type. In contrast, a physiological level of IL-1β treatment (0.01ng/ml) activated p-Src in neurons via AcPb in vitro. In addition, overexpression of AcPb in astrocytes was sufficient to induce p-Src mediated by IL-1β. Taken together, these results suggest that the restricted expression of AcPb in CNS neurons may mediate neuronal specific IL-1 pathways and outcomes, and that physiological and pathophysiological levels of IL-1β mediate particular neuronal functions via separate pathways.Ph. D.Includes abstractIncludes bibliographical referencesby Yangyang Huan
Molecular simulations of rheological, mechanical and transport properties of solid-fluid systems:
No full textIn this dissertation, two distinct but relevant systems are chosen as representatives of interesting solid-fluid systems. Molecular dynamics (MD) and Monte Carlo techniques are applied to investigate the rheological, mechanical and transport properties of these systems.
Firstly, polyethylene melt embedded with silica nanoparticles is examined to be of our interest. Since it is computationally impractical to model a complex system with a molecular description, a multiscale modeling approach, which combines both atomistic and mesoscale simulations, is employed to efficiently represent and study the polymer nanoparticle systems. Based on a coarse-grained force field for polyethylene, a novel method is developed for determining the solid-fluid interaction at the spherical interface. Our coarse grained model is designed to mimic 4 nm silica nanoparticles in polyethylene melt at 423K. A series of MD simulations are performed to investigate the factors that control the homogeneity of nanofillers inside polymer matrix, also in the presence of nonionic surfactants (short chain alcohols). The effects of nanoparticle filling fraction, polymer chain length, and relative sizes between nanoparticles and polymer chains on the particle dispersion are explored. In addition, a fundamental relationship is pursued between the microstructure and macroscopic properties (transport and rheological) of polymer nanoparticle composites.
In this work another method for determining the solid-fluid interaction parameter is presented: the experimental adsorption isotherms are used to validate the potential parameters. The rapid expansion of silica nanoparticle agglomerates in supercritical carbon dioxide (RESS process) is chosen to be the system of interest. The simulations show that the effective attraction between two identical nanoparticles is most prominent for densely hydroxylated particle surfaces that interact strongly with CO2 via hydrogen bonds, while it is significantly weaker for dehydroxylated particles. We also explore the shearing forces necessary to break an agglomerate in supercritical fluid. The agglomerate experiences deformation followed by elongation, and finally break-up. The calculated diffusion coefficient of CO2 is expected to be smaller than the experimental value, because the nanoparticle agglomerate hinders fluid movement. In the direction of shearing forces, the diffusion of CO2 shows a steep increase after the breakup, confirming the rupture of the agglomerate.Ph.D.Includes bibliographical references (p. 136-142)by Yangyang She
Self-Assembled Morphologies and Percolation Probability of Mixed Carbon Fillers in the Diblock Copolymer Template: Hybrid Particle-Field Molecular Dynamics Simulation
No full textThe self-assembly of polymer composites of mixed carbon fillers including single-walled carbon nanotube (SWCNT) and carbon black nanoparticles (CB NPs) in diblock copolymer (BCP) template are investigated using hybrid particle-field molecular dynamics simulations in this work. Simulations show, in agreement with experiments, that composites of BCP template with SWCNT have lower percolation threshold than that of BCP template with CB NPs. Moreover, the ratio between SWCNT and CB NPs has a strong influence on the percolation threshold of composites. The results of percolation probability show that adding more SWCNT (compared with CB NPs) to the BCP template could decrease the percolation threshold. However, a synergistic effect of percolation of the mixed carbon fillers in BCP template has been found. In particular, a nonlinear relation following the Boltzman function has been found, and the lowest percolation threshold exists with the volume ratio 4:1 (SWCNT/CB NPs) compared with the volume ratios of 1:1, 2:1, and 8:1 (SWCNT/CB NPs). The mixed carbon fillers also affect the morphologies of the BCP template, and the calculated radius of gyration of BCP shows that, in a higher concentration of the mixed fillers, the stretching of BCP is stronger, which results in the deformation of BCP template
sj-docx-1-aim-10.1177_09645284221085278 – Supplemental material for Manual acupuncture at ST36 attenuates rheumatoid arthritis by inhibiting M1 macrophage polarization and enhancing Treg cell populations in adjuvant-induced arthritic rats
No full textSupplemental material, sj-docx-1-aim-10.1177_09645284221085278 for Manual acupuncture at ST36 attenuates rheumatoid arthritis by inhibiting M1 macrophage polarization and enhancing Treg cell populations in adjuvant-induced arthritic rats by Nannan Yu, Fuming Yang, Xue Zhao, Yongming Guo, Yuan Xu, Guangchang Pang, Yinan Gong, Shenjun Wang, Yangyang Liu, Yuxin Fang, Kun Yu, Lin Yao, Hui Wang, Kuo Zhang, Baohu Liu, Zhenguo Wang, Yi Guo and Zhifang Xu in Acupuncture in Medicine</p
Towards robust malware detection
No full textThesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 45-48).A central challenge of malware detection using machine learning methods is the presence of adversarial variants, small changes to detectable malware that allow it to evade a model (i.e. be classified as benign). We take inspiration from adversarial variant generation methods in the continuous-valued image domain to introduce methods for malware in the binary domain. We incorporate these methods in the training of hardened models towards the goal of robustness against adversarial variants. Additionally, we provide visualization tools for analysis of hardened models. Our tools illustrate the difference in loss behavior between models trained with different methods, the effect of adversarial learning on the loss landscape of a model, and the effect of adversarial learning on the decision map of a model. The adversarial learning framework and the visualization tools in combination allow for the creation and understanding of robust models.by Alex Yangyang Huang.M. Eng
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