Browsing by Author "Zhang, Yan"

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    Comparison of shadow models and their impact on precise orbit determination of BeiDou satellites during eclipsing phases
    (2022-08-16) Zhang, Yan; Wang, Xiaoya; Xi, Kewei; Li, Zhen
    Abstract Solar radiation pressure (SRP) is an extremely critical perturbative force that affects the GNSS satellites’ precise orbit determination (POD). Its imperfect modelling is one of the main error sources of POD, whose magnitude is even to10−9 m/s2. The shadow factor (i.e., eclipse factor) is one crucial parameter of SRP, generally estimated by the cylindrical model, the conical model, or shadow models considering the Earth’s oblateness and the atmospheric effect, such as the Perspective Projection Method atmosphere (PPMatm) model and Solar radiation pressure with Oblateness and Lower Atmospheric Absorption, Refraction, and Scattering Curve Fit (SOLAARS-CF) model. This paper applies the former four shadow models to determine the corresponding precise orbit using BeiDou satellites’ ground-based observation, and then compared and assessed the orbit accuracy through Satellite Laser Ranging (SLR) validation and Inter-Satellite Link (ISL) check. The results show that the PPMatm model’s accuracy is equivalent to the SOLAARS-CF model. Compared with the conical shadow model, SLR validations show the orbit accuracy from the PPMatm and SOLAARS-CF model can be generally improved by 2–10 mm; ISL range check shows that the Root Mean Square (RMS) can be decreased by 2–7 mm. These results show that the shadow model in GNSS POD should fully consider the Earth’s oblateness and the atmospheric effect, especially for the perturbative acceleration higher than 10–10 m/s2. Graphical Abstract
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    Experimental Measurement of Diffusion Coefficient of Gaseous Solvents in Liquids
    (2021-05-12) Khalifi, Mohammad; Abedi, Jalal; Hassanzadeh, Hassan; Moore, Robert Gordon; Mehta, Sudarshan; Zhang, Yan; Johansen, Craig; Hejazi, Hossein
    The molecular diffusion coefficient is an important transport property used for modeling the diffusional mass transfer in many processes. In enhanced oil recovery from oil sands, molecular diffusion contributes to the mixing in the solvent-aided oil recovery techniques, and therefore, needs to be effectively captured for the successful modeling and performance prediction of the process. Despite the importance of diffusion coefficient in various engineering applications, there is an evident gap in the amount and quality of the diffusivity data available in the literature. This may be due to the complex nature of experimental measurements as well as the difficulties associated with analyzing the experimental data. In this study, a robust and reliable approach is developed for diffusivity measurement in systems of gaseous solvents and liquids. The developed methodology uses an analytical solution to the constant-pressure one-dimensional diffusion problem utilizing both the rate of gas dissolution and movement of the gas/liquid interface to estimate the molecular diffusivity coefficient. Moreover, a series of experimental setups have been designed, fabricated, and validated to maximize the accuracy of the experiments while satisfying the precision requirements for diffusivity measurements in systems of low soluble gases and liquids. The developed methodology was used to report the first datasets on diffusion coefficients of gaseous ethane in toluene and gaseous dimethyl ether in Athabasca bitumen and water. Also, an experimental method has been developed to measure the concentration dependency of the molecular diffusion coefficient of gases in liquids. The results indicated that the diffusion coefficient increases with the increase in test temperature. The pressure dependency, however, was explained by the effect of higher solvent concentration on the viscosity of the liquid mixture. Generally, lower viscosity at the diffusive boundary layer between gas and liquid resulted in higher diffusion coefficients. The developed methodology and the reported data have applications in the design and evaluation of solvent injection processes for heavy oil recovery.
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    Exploring Multiple Literacies and Identities of Children in a Mandarin-English Bilingual Program
    (2013-04-25) Zhang, Yan; Guo, Yan
    In Canadian schools, languages other than English and French are offered, such as Chinese, Spanish, German, and others. In order to help students in these programs develop to their fullest potentials, more research is necessary to explore the realities regarding students’ construction of identifications through multiple languages and literacies. Most previous studies on multilingual children’s literacies and identities have viewed literacy as a product and identity as an essential part of self associated with dimensions of culture, ethnicity, nationality, gender, religion, race, and generation. Little attention has been paid to the dynamic processes within children’s multiple literacy practices and the proliferation of cultural flows, modes of belonging, and new practices of citizenship that mobilize minds and bodies with identifications beyond nation-states. This study explores the multiplicity of how children in a Mandarin-English bilingual program become literate and how they form their sense of identities in a dynamic process. The study draws from a rhizomatic framework of transculturation, transnationalism, translanguaging and poststructural perspectives of literacies and identities as processes of becoming. Data for the study were collected by multiple methods: 1) classroom observations of eight students across their academic years of grade five and six, 2) semi-structured interviews with their parents, teachers, and the program coordinator, 3) students’ documents and artifact collection, and 4) additional conversations and email communications with the students. Results indicate that the multilingual children in the study exceeded language boundaries and revealed highly creative uses of languages. They were engaged in complex, multi-layered, fluid, and context-dependent multilingual communication in different social networks, challenged the dominant discourse of any fixed and hyphenated identity, and took on transcultural and transnational identities that allowed for comfortable circulation among different worlds. Meanwhile, their life experiences, virtual and actual, assembled in and across different contexts and contributed to their reading, reading the world, and self. Implications of this research suggest the need to expand poststructural perspectives of literacies and identities to include multilingual and multicultural issues. Educators need to recognize they are teaching far more than the letters of the alphabet and unfold children’s multiple and mobile identities to explore new possibilities for life. This research also provides insights to inform policy-makers concerning heritage language and bilingual teaching in Canada.