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Authors: Zhang, Xinshuai | Cai, Wei | Wang, Bei | Hou, Yuguo

Article Type: Research Article

Abstract: Most of global navigation satellite systems (GNSS) are transmitting three or even more frequency signals. Narrow lane combinations of these multi-frequency observations are characterized by short wave length, high precision and have been widely used in positioning and orientating. In this work, the optimal narrow lane combinations were theoretically investigated to improve the solution precision. To this end, the basic multi-frequency linear combination model was introduced and two key factors (i.e. noise factor and lane number) were defined. On this basis, two parameters SPI (Solution Precision Indicator) and SPI rel (Relative Solution Precision Indicator) were derived to evaluate solution precision. …Then, the optimal dual-frequency and triple frequency conditions were derived theoretically, which was verified by BDS (BeiDou Navigation System) experiment. The obtained results show that the linear combinations satisfying optimal condition can lead to a higher positioning and orientating precision and the precision increased with more frequencies. Show more

Keywords: GNSS, optimal narrow lane combinations, GNSS orientating

DOI: 10.3233/JCM-180876

Citation: Journal of Computational Methods in Sciences and Engineering, vol. 19, no. 2, pp. 337-351, 2019

Authors: Zhang, Xinshuai | Cai, Wei | Wang, Bei | Hou, Yuguo

Article Type: Research Article

Abstract: The narrow lane carrier phase combinations, especially in the case of short baseline, are commonly used to obtain high orientating accuracy using the multi-frequency GNSS (Global Navigation Satellite System) due to their ability to mitigate measurement noise and multipath. However, after reviewing the errors in solutions of NL (narrow lane) combinations and the original combination (combine carrier phase data independently), it is found that the original combination always has a better performance than all NL combinations with positive coefficients regardless of which navigation system is used and how many frequencies are used. To achieve this, the observation equations of linear …combination and original combination are first considered with emphasis on the relevant errors and the measurement noise mitigating ability. Then this paper derives the solutions of those combinations and focuses on their performance comparison in aspects of solution accuracy and systematic errors. Finally, the theoretical developments are verified with BDS data and the advantages of the original combination are summarized and discussed. Show more

Keywords: GNSS orientating, original combination, narrow lane combinations, multi-frequency GNSS, solution precision

DOI: 10.3233/JCM-190016

Citation: Journal of Computational Methods in Sciences and Engineering, vol. 19, no. 3, pp. 681-694, 2019

Authors: Zhao, Qianhua | Roberts, Rosebud O. | Ding, Ding | Cha, Ruth | Guo, Qihao | Meng, Haijiao | Luo, Jianfeng | Machulda, Mary M. | Shane Pankratz, V. | Wang, Bei | Christianson, Teresa J.H. | Aakre, Jeremiah A. | Knopman, David S. | Boeve, Bradley F. | Hong, Zhen | Petersen, Ronald C. | and the Shanghai Aging Study (SAS), the Mayo Clinic Study of Aging (MCSA)

Article Type: Research Article

Abstract: Background and Objectives: It remains unknown whether the association between diabetes mellitus (DM) and cognitive function differs in Eastern and Western populations. This study aimed to elucidate whether DM is associated with worse cognitive performance in both populations. Methods: The Shanghai Aging Study (SAS) and the Mayo Clinic Study of Aging (MCSA) are two population-based studies with similar design and methodology in Shanghai, China and Rochester, MN, USA. Non-demented participants underwent cognitive testing, and DM was assessed from the medical record. Separate analyses were performed in SAS and MCSA regarding the association between DM and cognitive performance. Results: A total …of 3,348 Chinese participants in the SAS and 3,734 American subjects in the MCSA were included. Compared with MCSA subjects, SAS participants were younger, less educated, and had lower frequency of vascular disease, APOE ɛ 4 carriers and obesity. Participants with DM (compared to non-DM participants) performed significantly worse on all the cognitive domains in both the SAS and MCSA. After adjustment for age, gender, education, and vascular covariates, DM was associated with worse performance in executive function (β =−0.15, p  = 0.001 for SAS, and β =−0.10, p  = 0.008 for MCSA) in the total sample and in the cognitively normal sub-sample. Furthermore, DM was associated with poor performance in visuospatial skills, language, and memory in the SAS, but not in the MCSA. Conclusions: Diabetes is associated with cognitive dysfunction and, in particular, exerts a negative impact on executive function regardless of race, age, and prevalence of vascular risk factors. Show more

Keywords: Cognition, cross-sectional studies, diabetes mellitus, executive function

DOI: 10.3233/JAD-150073

Citation: Journal of Alzheimer's Disease, vol. 47, no. 1, pp. 167-176, 2015