VTechWorks staff will be away for the Thanksgiving holiday beginning at noon on Wednesday, November 27, through Friday, November 29. We will resume normal operations on Monday, December 2. Thank you for your patience.

Browsing by Author "Ma, Xiaoyan"

Now showing 1 - 2 of 2
  • Thumbnail Image
    An Integrative Literature Review of Self-Directed Learning in Higher Education
    Ma, Xiaoyan (Virginia Tech, 2017-05-05)
    As a prerequisite for all adult learners in life-long learning, self-directed learning has been constantly discussed since the early 1960s. However, in what manner research operationalizes the concepts and what similarities occur across the empirical studies and theoretical studies are still ambiguous. The purpose of this study is to employ an integrative literature review to investigate and disentangle various interpretations of self-directed learning by identifying how the topic is defined and what competencies and strategies are needed for a highly self-directed learner. This is a six-phase study, including: 1) problem formulation; 2) data collection; 3) problem re-formulation; 4) data evaluation; 5) data collection; and 6) presentation of the findings. This study provided a comprehensive perspective of self-directed learning in a dynamically expanding process to include multifaceted interpretations of the topic and advanced research in self-directed learning in an updated, enriched learning environment. Specifically, the researcher updated the evidence for self-directed learning to date, identified all of the potential dimensions of self-directed learning that distinguish a highly-directed self-directed learner and the related instructional strategies, and made suggestions for the future direction of research on the topic.
  • Thumbnail Image
    Occurrence of Free Amino Acids in the Source Waters of Zhejiang Province, China, and Their Removal and Transformation in Drinking Water Systems
    Yang, Yulong; Yu, Qi; Zhou, Ruonan; Feng, Jiao; Zhang, Kejia; Li, Xueyan; Ma, Xiaoyan; Dietrich, Andrea M. (MDPI, 2019-12-24)
    Free amino acids (FAAs) are key components of the global nitrogen cycle and important disinfection byproduct (DBP) precursors. The knowledge gap of FAA occurrence in source and engineered water is discussed in this paper. Solid phase extraction and post column derivatization was combined with gas chromatography–mass spectrometry to simultaneously detect μg/L concentrations of FAAs. This method efficiently detects alanine (Ala), threonine (Thr), serine (Ser), valine (Val), leucine (Leu), isoleucine (Ile), proline (Pro), aspartic (Asp), phenylalanine (Phe), and glutamic acid (Glu) with good linearity, accuracy, and precision. An investigation of FAAs in surface waters in Zhejiang Province found concentrations of 1.48–14.73 μg/L Ala, 0.20–2.39 μg/L Thr, 0.41–7.84 μg/L Val, 0.21–6.86 μg/L Ser, 0.11–4.16 μ;g/L Leu, 0.57–1.54 μg/L Ile, 0.24–8.06 μg/L Pro, 0.42–4.73 μg/L Asp, 0.30–3.01 μg/L Phe, and 0.12–3.83 μg/L Glu. Phe and tyrosine (Tyr) exhibited higher trichloromethane (TCM) formation (1029–1148 μg/mmolAA) than dichloroacetonitrile (DCAN) formation (333–347 μg/mmolAA). Asp and Glu demonstrated the opposite trend: higher DCAN (570–1106 μg/mmolAA) formation than TCM (137–506 μg/mmolAA).