Browsing by Author "Zhang, Chi"

Now showing 1 - 4 of 4
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    Assessing the Effect of Global Travel and Contact Restrictions on Mitigating the COVID-19 Pandemic
    Lai, Shengjie; Ruktanonchai, Nick W.; Carioli, Alessandra; Ruktanonchai, Corrine W.; Floyd, Jessica R.; Prosper, Olivia; Zhang, Chi; Du, Xiangjun; Yang, Weizhong; Tatem, Andrew J. (2021-07)
    Travel restrictions and physical distancing have been implemented across the world to mitigate the coronavirus disease 2019 (COVID-19) pandemic, but studies are needed to understand their effectiveness across regions and time. Based on the population mobility metrics derived from mobile phone geolocation data across 135 countries or territories during the first wave of the pandemic in 2020, we built a metapopulation epidemiological model to measure the effect of travel and contact restrictions on containing COVID-19 outbreaks across regions. We found that if these interventions had not been deployed, the cumulative number of cases could have shown a 97-fold (interquartile range 79-116) increase, as of May 31, 2020. However, their effectiveness depended upon the timing, duration, and intensity of the interventions, with variations in case severity seen across populations, regions, and seasons. Additionally, before effective vaccines are widely available and herd immunity is achieved, our results emphasize that a certain degree of physical distancing at the relaxation of the intervention stage will likely be needed to avoid rapid resurgences and subsequent lockdowns. (C) 2021 THE AUTHORS. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company.
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    Characterization of the transcriptional divergence between the subspecies of cultivated rice (Oryza sativa)
    Campbell, Malachy T.; Du, Qian; Liu, Kan; Sharma, Sandeep; Zhang, Chi; Walia, Harkamal (2020-06-08)
    Background Cultivated rice consists of two subspecies, Indica and Japonica, that exhibit well-characterized differences at the morphological and genetic levels. However, the differences between these subspecies at the transcriptome level remains largely unexamined. Here, we provide a comprehensive characterization of transcriptome divergence and cis-regulatory variation within rice using transcriptome data from 91 accessions from a rice diversity panel (RDP1). Results The transcriptomes of the two subspecies of rice are highly divergent. Japonica have significantly lower expression and genetic diversity relative to Indica, which is likely a consequence of a population bottleneck during Japonica domestication. We leveraged high-density genotypic data and transcript levels to identify cis-regulatory variants that may explain the genetic divergence between the subspecies. We identified significantly more eQTL that were specific to the Indica subspecies compared to Japonica, suggesting that the observed differences in expression and genetic variability also extends to cis-regulatory variation. Conclusions Using RNA sequencing data for 91diverse rice accessions and high-density genotypic data, we show that the two species are highly divergent with respect to gene expression levels, as well as the genetic regulation of expression. The data generated by this study provide, to date, the largest collection of genome-wide transcriptional levels for rice, and provides a community resource to accelerate functional genomic studies in rice.
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    Plan of Study Management System
    Zhang, Chi; Wang, Haosu; Zhang, Lihui; Fan, Jiahui; Cai, Zihao (2022-05-04)
    New students in the CSA-Meng program often get overwhelmed by the different concentrations and courses. They also lack a good mechanism to get course information. Thus they could easily make wrong decisions when designing their plan of study. The POS management system is designed to help students get course information, plan their courses and generate their own POS. They only need to answer a few questions before the system generates some plausible qualified POS for them. The system can also help students to check if their manually added POS and course list meet the requirements of the department.
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    A SiC-Based Liquid-Cooled Electric Vehicle Traction Inverter Operating at High Ambient Temperature
    Zhang, Chi; Srdic, Srdjan; Lukic, Srdjan; Wang, Jun; Burgos, Rolando (China Power Supply Society, 2022-06-30)
    This paper describes the design process of a high-power-density 100 kW (34 kW/L) traction inverter for electric vehicles, operating at an ambient temperature of 105 °C. A detailed thermal analysis is performed based on the thermal behavior of the switching devices, and the results are used to estimate the semiconductor device junction temperature and to determine the requirements of the cooling system to achieve the target power level. A high-temperature gate drive board aiming for reliable system operation in electric vehicles is developed. An overcurrent protection scheme based on parasitic inductance between the power source and the Kelvin source of the power module has been implemented. A dc-link decoupling snubber circuit is designed numerically based on a detailed forth-order high-frequency equivalent circuit of a double pulse test circuit. The approach to optimize the snubber circuit, not only for the voltage spike suppression but also for good thermal performance, is proposed. Finally, a hardware prototype with SiC power modules has been built and tested at 60 kW continuous power and 100 kW for 20 seconds at 105 °C ambient temperature and 65 °C inlet coolant temperature.