金钱榕提取物抑制3T3-L1脂肪细胞抗脂肪沉积研究(英文)

研究目的:对两个品种金钱榕(var.deltoidea和var.angustifolia)叶片提取物抑制3T3-L1脂肪细胞脂肪沉积进行研究,为基于金钱榕的抗肥胖功能产品开发提供理论基础。研究方法:用甲醇和水分别对两个品种金钱榕的叶片进行提取,并分别分析了提取物中的总黄酮含量(TFC)和总酚含量(TPC)。通过MTT法确定提取物对3T3-L1脂肪细胞的最大无毒剂量(MNTD)。然后,通过油红O染色和吸光度测定来定性和定量研究提取物对抗脂肪细胞脂肪沉积的作用。重要结论:金钱榕两个品种deltoidea和angustifolia的甲醇提取物中的TFC含量分别为1.36和1.97 g QE/100 g DW,水提取物中的TPC含量分别为5.61和2.73 g GAE/100 g DW。金钱榕deltoidea品种的甲醇和水提取物对3T3-L1细胞的MNTD分别为(300.0±28.3)和(225.0±21.2)μg/ml,而angustifolia品种的MNTDs则较低(其甲醇和水提取物的MNTDs分别为(60.0±2.0)和(8.0±1.0)μg/ml)。金钱榕两个品种的甲醇提取物和angustifolia品种的水提取物在MNTD或1/2MNTD的浓度下,均具有显著抑制前脂肪细胞的成熟的作用。因此,根据其抑制成熟脂肪细胞形成的结果可以得出金钱榕叶片提取物具有潜在的抗肥胖效果。     

Student perceptions of facilitators’ social congruence,use of expertise and cognitive congruence in problem-based learning

In problem-based learning (PBL), the role of a tutor or facilitator is different from what is typically considered as the role of a traditional teacher. In addition to being a subject-matter expert, the facilitator is also expected to be ‘socially’ and ‘cognitively congruent’. In this study, we analyze the survey responses from more than 10,000 students in order to better understand their perceptions of what makes a good or poor facilitator, and to identify specific qualities related to social congruence, cognitive congruence and use of expertise. Students’ comments for the highest and lowest scoring groups of facilitators were analyzed qualitatively using inductive data analysis strategies. The following themes were identified: for social congruence—facilitator personality, relating to students, professionalism, motivating students, and learning environment; for cognitive congruence—scaffolding learning, and communication skills; for use of expertise—content knowledge and experience, and stretching students’ learning. Coding of students’ feedback also demonstrated that students most frequently commented on issues related to facilitators’ social congruence. Our findings indicate that social congruence encompasses skills which facilitators may improve on. We also argue that understanding students’ perspectives is critical especially in a learner-centred approach such as PBL and therefore propose that our findings provide useful input for the professional development of PBL facilitators.     

The social practice of learning: a craft for the 21st century

This article argues that the social practice of learning (SPL), involving life-long learning, meta-learning, deep reflection, and dialogue in a community, should be the distinguishing knowledge base of schools in the twenty-first century. This article also analyses the strategies and challenges of the recent education reforms in Singapore through the lens of an SPL education paradigm. Although the Singapore government has done much to train teachers, trim syllabi and introduce new ways of teaching and learning, such as project work, the real challenge is to go beyond the provision of structural changes to the substance of the epistemological reform.     

What students learn in problem-based learning: a process analysis

This study aimed to provide an account of how learning takes place in problem-based learning (PBL), and to identify the relationships between the learning-oriented activities of students with their learning outcomes. First, the verbal interactions and computer resources studied by nine students for an entire PBL cycle were recorded. The relevant concepts articulated and studied individually while working on the problem-at-hand were identified as units of analysis and counted to demonstrate the growth in concepts acquired over the PBL cycle. We identified two distinct phases in the process—an initial concept articulation, and a later concept repetition phase. To overcome the sample-size limitations of the first study, we analyzed the verbal interactions of, and resources studied, by another 35 students in an entire PBL cycle using structural equation modeling. Results show that students’ verbal contributions during the problem analysis phase strongly influenced their verbal contributions during self-directed learning and reporting phases. Verbal contributions and individual study influenced similarly the contributions during the reporting phase. Increased verbalizations of concepts during the reporting phase also led to higher achievement. We found that collaborative learning is significant in the PBL process, and may be more important than individual study in determining students’ achievement.     

Analysis of streamwise conduction in forced convection of microchannels using fin approach

The effects induced by streamwise conduction on the thermal characteristics of forced convection for single-phase liquid flow in rectangular microchannel heat sinks under imposed constant wall temperature have been studied. By employing the fin approach in the first law of analysis, models with and without streamwise conduction term in the energy equation were developed for hydrodynamically and thermally fully-developed flow under local thermal non-equilibrium for the solid and fluid phases. These two models were solved to obtain closed form analytical solutions for the fluid and solid temperature distributions and the analysis emphasized details of the variations induced by the streamwise conduction on the fluid temperature distributions. The effects of the Peclet number, aspect ratio, and thermal conductivity ratio on the thermal characteristics of forced convection in microchannel heat sinks were analyzed and discussed. This study reveals the conditions under which the effect of streamwise conduction is significant and should not be neglected in the forced convective heat transfer analysis of microchannel heat sinks.     

Institutional Support for Handheld Computing: Clinical and Educational Lessons Learned

Handheld computing devices, or personal digital assistants (PDAs), are used often in the health care setting. They provide a convenient way to store and carry either personal or reference information and can be used to accomplish other tasks associated with patient care. This article reports clinical and educational lessons learned from a longitudinal institutional initiative designed to provide medical students with PDAs to facilitate patient care and assist with clinical learning.     

Interpreting unfamiliar graphs: A generative, activity theoretic model

Research on graphing presents its results as if knowing and understanding were something stored in peoples' minds independent of the situation that they find themselves in. Thus, there are no models that situate interview responses to graphing tasks. How, then, we question, are the interview texts produced? How do respondents begin and end utterances? And, what is the relation between words and gestures used as part of the communication? Based on a database developed in two studies with research scientists (N = 37), we developed a theoretical framework using cultural-historical activity theory for understanding the texts produced during interviews. Our framework addresses three major findings, whose implications are discussed in the paper. First, the interview text is the contingent and situated product of the entire activity system, including interviewer and other aspects of the setting; the interview text can therefore not be reduced to the cognitive properties of the individual interviewee. Second, the interpretation unfolds in time, shaping the way the graph itself is perceived; unlike a written text that accompanies a graph, the verbally produced interview text therefore has to be analyzed through a moving interpretive window without recourse to subsequently produced talk. Third, gestures, speech, and the perceptual aspects of the graph currently salient to the interviewee, have to be understood as expressions that are irreducible to one another, requiring comprehensive research reports to present all modes of concurrent expression.     

Personal Bias or Government Bias? Testing the Hostile Media Effect in a Regulated Press System

This study examines the hostile media effect in relation topartisans’ perception of the slant of news coverage ina highly regulated press environment—Singapore. We foundthat partisans in Singapore perceived unbiased news to be infavor of the other side, while the nonpartisans perceived thesame news to be neutral. Our findings show that hostile mediaeffects can persist in a restricted press environment wherepeople are aware of the government's control of media coverage.We also found that partisans’ awareness of the government'scontrol of media information contributed to their perceptionof the article slant as well. Received for publication May 9, 2006. Accepted for publication December 5, 2006.     

Cultivating sustained teachers’ professional learning within a centralised education system

This study investigates how sustained professional learning for teachers within a centralised system was cultivated. Specifically, the sustained professional learning was initiated by officers from the headquarters (HQ) and involved interested teachers across schools in Singapore. Qualitative instruments were used to collect and analyse the data in examining the partnerships perceived by the participants. The enablers responsible to bring about sustained professional learning are proposed. A contribution of this study is to clarify how resources in the HQ and its schools can be bridged. Deliberate bridging of resources is critical particularly at the initial stage of the partnerships. This bridging is made possible through dedicated appointed champions. The appointed champions are passionate about the educational innovations and are willing to invest their time to understand the teachers’ needs. This paper argues that the enablers can offer opportunities for lateral networks to be forged within a hierarchical system.