568 research outputs found
Complexity of branch-and-bound and cutting planes in mixed-integer optimization
No full textWe investigate the theoretical complexity of branch-and-bound (BB) and cutting plane (CP) algorithms for mixed-integer optimization. In particular, we study the relative efficiency of BB and CP, when both are based on the same family of disjunctions. We extend a result of Dash (International Conference on Integer Programming and Combinatorial Optimization (IPCO), pp. 145-160, 2002) to the nonlinear setting which shows that for convex 0/1 problems, CP does at least as well as BB, with variable disjunctions. We sharpen this by giving instances of the stable set problem where we can provably establish that CP does exponentially better than BB. We further show that if one moves away from 0/1 sets, this advantage of CP over BB disappears; there are examples where BB finishes in O(1) time, but CP takes infinitely long to prove optimality, and exponentially long to get to arbitrarily close to the optimal value (for variable disjunctions). We next show that if the dimension is considered a fixed constant, then the situation reverses and BB does at least as well as CP (up to a polynomial blow up factor), for quite general families of disjunctions. This is also complemented by examples where this gap is exponential (in the size of the input data)
sj-docx-1-eso-10.1177_23969873221126000 – Supplemental material for Prognostic significance of atrial cardiopathy in patients with acute ischemic stroke
No full textSupplemental material, sj-docx-1-eso-10.1177_23969873221126000 for Prognostic significance of atrial cardiopathy in patients with acute ischemic stroke by Yueyang Wu, Xiaomeng Yang, Jing Jing, Xia Meng, Zixiao Li, Yuesong Pan, Yong Jiang, Hongyi Yan, Xinying Huang, Liping Liu, Xingquan Zhao, Yilong Wang, Hao Li and Yongjun Wang in European Stroke Journal</p
The Transformation of Urban Vegetable Retail in China: Wet Markets, Supermarkets, and Informal Markets in Shanghai
No full textSingapore Management University Office of ResearchThis research is supported by a research grant from the Singapore Management University’s Office of Research to the first author. We thank Professor JIANG Changjian of Fudan University and Ms. Lu Zhihua of Wujiaochang Town Government for facilitating the fieldwork. An earlier version of the paper was presented at the Sixth Annual Workshop of the Asian Network of Scholars of Local China (ANSLoC). We are grateful to participants of the workshop, including Professors Jae Ho Chung, Tse-Kang Leng, John DONALDSON, Hongyi Lai, Phil Hsu, Wai-Keung Chung, Eric Mobrand, and James Tang, for their valuable comments and suggestions. The authors are solely responsible for any errors.</p
Suppression of vortex shedding in the wake of a circular cylinder through high-frequency in-line oscillation
No full textThis paper presents a new flow control approach to suppress the vortex shedding in the wake of a circular cylinder through high-frequency oscillation. The circular cylinder is forced to oscillate in the streamwise direction at high-frequency and low amplitude, corresponding to a high Stokes number (b ¼ 100–1000) and low Keulegan–Carpenter number (KC¼ 0.001–4). Two-dimensional (2-D) and three-dimensional (3-D) direct numerical simulations of an oscillating circular cylinder in steady current have been carried out in the parameter space of KC, Rec, and b. Our numerical results show that when the flow remains in the two-dimensional vortex shedding regime, the cylinder wake sequentially experiences transitions from the vortex shedding regime to the suppression of the vortex shedding regime and finally to the symmetry breaking regime, with increasing KC. Corresponding wake characteristics and variations of hydrodynamic forces over the three wake regimes are explored. Three quantities that represent shear-layer characteristics, including the length of separating shear layers, the circulation of shear layers and wake recirculation length, reach maxima at the onset of suppression. The physical mechanisms for the suppression of vortex shedding and occurrence of symmetry breaking are also explained. Once the flow becomes 3-D, vortex shedding from the cylinder cannot be suppressed, primarily because the outer shear layers induced by the steady approaching flow are enhanced in 3-D flows. The cylinder oscillation over the frequency range investigated in the present study delays wake transition to 3-D. The cylinder oscillation alters the 3-D vortical structure and its spanwise wavelength significantly.Dan Pang, Liang Cheng, Hongyi Jiang, Feifei Tong, Hongwei A
DNS results of forces on a circular cylinder (data) May2022
No full textDNS results of forces on a circular cylinder (data) May202
Improving economics education outcomes through gamification and simulation
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 (page 49).Presented here is a thorough attempt to translate concepts in microeconomics to games in an attempt to improve educational outcomes at the high school and college level. Two different kinds of educational economics games are explored and described in detail, with the second having been implemented using the Unity game engine. Playtesting was done with both students and educators, in order to improve gameplay experience and ascertain how games can be best implemented within the economics curriculum. Further improvements to gameplay and educational effectiveness of the project are explored for possible future work done on the topic.by Hongyi Shi.M. Eng
Exogenous P compounds differentially interacted with N availability to regulate enzymatic activities in a meadow steppe
No full textIncreased inputs of ecosystem nitrogen (N) and phosphorus (P) may affect the activity of soil enzymes that play essential roles in the metabolization of carbon (C), N and P for microbial growth. However, the associations between soil enzymatic activities and N and P availability remain poorly understood. We conducted a study in a meadow steppe to elucidate the effects of the addition of N, as ammonium nitrate (NH₄NO₃3), and two forms of P with contrasting solubility, comprising monopotassium phosphate (KH₂PO₄) and the less soluble triple superphosphate (Ca(H₂PO₄)₂, on activity of β-glucosidase (BG), N-acetyl-glucosaminidase (NAG) and acid and alkaline phosphomonoesterases (PMEs). In general, there was a positive effect of N on BG, NAG and alkaline PME activity as a result of enhanced soil N availability, plant-microbe nutrient competition and plant P uptake. Addition of KH₂2PO₄ increased activity of BG, NAG and alkaline PME, but had no impact on acid PME activity. Addition of Ca(H₂PO₄)2 increased NAG activity, but only increased activity of BG and alkaline PME with the addition of N. Concentration of soil available P and microbial biomass P increased with added P, particularly KH₂PO₄. These results provide the first evidence for the N- and P-mediated stimulation of microbial activity depending on the chemical form of added P in this ecosystem. Relationships between activity of BG and NAG, and between that of NAG and PME, were allometric, indicating disproportionate changes in activity of these soil enzymes. This further suggests shifts in microbial acquisition of C, N and P along with increases in availability of N and P that may potentially affect plant productivity. We conclude that scenarios of global environmental change, in which ecosystem availability of N and P is affected, may result in variable activity responses among soil enzymes, and the chemical form of P input should be considered as an important factor influencing meadow steppe grassland ecosystem function
Artifact for MobiCom'23: Virtual Device Farms for Mobile App Testing at Scale: A Pursuit for Fidelity, Efficiency, and Accessibility
No full textThis dataset contains the anonymized failure data collected from our physical and device farms over a three-month period. The failure data involves 5,918 physical devices as well as 5,918 virtualized devices running on ARM commodity servers.
For more details, please visit our website (Android-Emulation-Testing.github.io) or read our paper:
[MobiCom'23] Virtual Device Farms for Mobile App Testing at Scale: A Pursuit for Fidelity, Efficiency, and Accessibility
If you use our dataset in your work, please reference it using:
@inproceedings {lin2022virtual,
author = {Lin, Hao and Qiu, Jiaxing and Wang, Hongyi and Li, Zhenhua and Gong, Liangyi and Gao, Di and Liu, Yunhao and Qian, Feng and Zhang, Zhao and Yang, Ping and Xu, Tianyin},
title = {{Virtual Device Farms for Mobile App Testing at Scale: A Pursuit for Fidelity, Efficiency, and Accessibility}},
booktitle = {The 29th Annual International Conference on Mobile Computing and Networking (ACM MobiCom'23)},
year = {2023},
publisher = {ACM}
}Version 1.0.2: This update adds reference information and fixes Colab icon issues
Improving PET Image Using U-net and MRI
No full textThis study aims to develop a modified deep learning convolutional network algorithm, a U-net, to improve the quality of a PET image. In this study, the U-net was designed to accept a PET image and a corresponding MRI images as inputs, and make a prediction of improved PET image based on the inputs. The PET images are created by tracers that are bound in different concentrations to different tissue types, such as [18F]FDG or a tracer designed to detect amyloid plaques. The MRI image should be taken either at the same time or at a recent (prior or post) time when the PET image is taken. A U-net that was originally designed to predict black and white binary segmentation maps was constructed. It was then modified to output grey-scale non binary images with pixels of different color intensities.
Digital phantoms were used to input image datasets for U-net. To improve upon the limitation of previous studies in this area, this study used relatively realistic digital phantoms to generate datasets (as opposed to using clinical data, physical phantoms, or simplistic digital phantoms). The modified U-nets were then trained with generated training datasets using a PC with Intel Core i7-9700K CPU, NVIDIA GTX2080Ti GPU, and 16GB memory. Each resulting trained U-net was used to process 1000 random datasets, and the results were evaluated using DSC or SSIM index based on the output image type of U-nets to see if the predictions are improved compared with the input
The trained U-net successfully produced improved images of PET tracer distribution, and showed that it is possible for a U-net to locate irregular lesions of varying textures. This result also showed that a U-net trained with simulated data can produce practical results (predictions with statistically significant improvement) when operating on images resulted from a realistic digital phantom.
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