Certain hexavalent chromium (Cr^(6+)) compounds when administered via inhalation at high doses have the potential to induce lung tumors in humans and experimental animals. Trivalent chromium (Cr^(3+)) is an essential ...Certain hexavalent chromium (Cr^(6+)) compounds when administered via inhalation at high doses have the potential to induce lung tumors in humans and experimental animals. Trivalent chromium (Cr^(3+)) is an essential human and animal nutrient at levels of 50 to 200 μg/day. Recent data have shown that the human body is able to reduce Cr^(6+) to Cr^(3+). This reduction occurs in bodily fluids such as gastric juice, epithelial lining fluid of.the respiratory tract, blood, and other fluids. Secondary reduction occurs at the cellular level by the cytosol, mitochondria, and microsomes. Thus, at low levels of exposure hexavalent chromium ions are reduced befor the 6+ ions can interact with DNA unless the dose is sufficient to overwhelm the body's reduction capacity. This paper summarizes the available data concerning the reducing ability of the body and formulates the steps in the mechanism of cancer induction. These steps include: (1) only certain Cr^(6+) compounds have the capacity to interact with cellular components; (2) Cr^(6+) is reduced by body fluids and excess Cr^(6+) enters the cell (Cr^(3+) is poorly absorbed across membranes); (3) cellular organelles and the cytoplasm reduce Cr^(6+) to Cr^(3+); (4) excess Cr^(6+) can enter the nucleus; (5) Cr^(6+) reduction through 5+ and 4+ to 3+ has a potential to interact with the DNA molecule; and (6) if unrepaired, this DNA damage can lead to cancer induction. On the basis of current evidence Cr^(6+) has a threshold for carcinogenic potential in humans that is greater than the current TLV. 1990 Academic Press. Inc.展开更多
This study describes the planning process of a major multi-disciplinary research project that aims to enhance effectiveness of the Higher Degree Research （HDR） training process in computing-related disciplines by ap...This study describes the planning process of a major multi-disciplinary research project that aims to enhance effectiveness of the Higher Degree Research （HDR） training process in computing-related disciplines by applying the threshold concept theories and framework. Two specific disciplines, the computer science and information systems were chosen for the study that closely represents the two ends of a wide range of computing discipline spectrum within the faculties of science, engineering, business and education. The ultimate goal of the above major project, when completed, is to enhance productivity of research training process in computing schools. The foreshadowed problem is that for many of HDR students it takes a long time to produce a specific result expected to be done in much shorter periods of time; and yet at some stage the student seems to get over this hurdle almost overnight. By adopting a threshold concept framework this study extends existing studies in the above area by specifically targeting HDR process in computing disciplines, and provides plans for a wide range of studies that will ideally lead to identification of threshold concept for HDR students in computing disciplines. The issue under development in the current study is how can the process of overcoming the above hurdles be facilitated？ How can the productivity of various resources utilized during the above long and frustrating waiting periods be increased by shortening the waiting times？展开更多
A new classification algorithm for web mining is proposed on the basis of general classification algorithm for data mining in order to implement personalized information services. The building tree method of detecting...A new classification algorithm for web mining is proposed on the basis of general classification algorithm for data mining in order to implement personalized information services. The building tree method of detecting class threshold is used for construction of decision tree according to the concept of user expectation so as to find classification rules in different layers. Compared with the traditional C4.5 algorithm, the disadvantage of excessive adaptation in C4.5 has been improved so that classification results not only have much higher accuracy but also statistic meaning.展开更多
2015年2月,美国大学与研究图书馆协会(ACRL)正式发布《高等教育信息素养框架》(Framework for Information Literacy for Higher Education)(以下简称《框架》)。它是国际范围内信息素养教育的重要指导性文件,发布后立即引起国际信息素...2015年2月,美国大学与研究图书馆协会(ACRL)正式发布《高等教育信息素养框架》(Framework for Information Literacy for Higher Education)(以下简称《框架》)。它是国际范围内信息素养教育的重要指导性文件,发布后立即引起国际信息素养教育界的强烈反响,国内业界人士也纷纷对它的内容进行分析解读。本文对《框架》的理论基础与具体内容进行反思,认为《框架》的理论基础——"阈概念"与"元素养"并不完全契合信息素养教育实践,而且《框架》以学术研究而非信息素养为出发点,强调学术信息,弱化了学术信息以外的信息内容。除此之外,《框架》还忽视了信息过载的问题。展开更多
文摘Certain hexavalent chromium (Cr^(6+)) compounds when administered via inhalation at high doses have the potential to induce lung tumors in humans and experimental animals. Trivalent chromium (Cr^(3+)) is an essential human and animal nutrient at levels of 50 to 200 μg/day. Recent data have shown that the human body is able to reduce Cr^(6+) to Cr^(3+). This reduction occurs in bodily fluids such as gastric juice, epithelial lining fluid of.the respiratory tract, blood, and other fluids. Secondary reduction occurs at the cellular level by the cytosol, mitochondria, and microsomes. Thus, at low levels of exposure hexavalent chromium ions are reduced befor the 6+ ions can interact with DNA unless the dose is sufficient to overwhelm the body's reduction capacity. This paper summarizes the available data concerning the reducing ability of the body and formulates the steps in the mechanism of cancer induction. These steps include: (1) only certain Cr^(6+) compounds have the capacity to interact with cellular components; (2) Cr^(6+) is reduced by body fluids and excess Cr^(6+) enters the cell (Cr^(3+) is poorly absorbed across membranes); (3) cellular organelles and the cytoplasm reduce Cr^(6+) to Cr^(3+); (4) excess Cr^(6+) can enter the nucleus; (5) Cr^(6+) reduction through 5+ and 4+ to 3+ has a potential to interact with the DNA molecule; and (6) if unrepaired, this DNA damage can lead to cancer induction. On the basis of current evidence Cr^(6+) has a threshold for carcinogenic potential in humans that is greater than the current TLV. 1990 Academic Press. Inc.
文摘This study describes the planning process of a major multi-disciplinary research project that aims to enhance effectiveness of the Higher Degree Research （HDR） training process in computing-related disciplines by applying the threshold concept theories and framework. Two specific disciplines, the computer science and information systems were chosen for the study that closely represents the two ends of a wide range of computing discipline spectrum within the faculties of science, engineering, business and education. The ultimate goal of the above major project, when completed, is to enhance productivity of research training process in computing schools. The foreshadowed problem is that for many of HDR students it takes a long time to produce a specific result expected to be done in much shorter periods of time; and yet at some stage the student seems to get over this hurdle almost overnight. By adopting a threshold concept framework this study extends existing studies in the above area by specifically targeting HDR process in computing disciplines, and provides plans for a wide range of studies that will ideally lead to identification of threshold concept for HDR students in computing disciplines. The issue under development in the current study is how can the process of overcoming the above hurdles be facilitated？ How can the productivity of various resources utilized during the above long and frustrating waiting periods be increased by shortening the waiting times？
文摘A new classification algorithm for web mining is proposed on the basis of general classification algorithm for data mining in order to implement personalized information services. The building tree method of detecting class threshold is used for construction of decision tree according to the concept of user expectation so as to find classification rules in different layers. Compared with the traditional C4.5 algorithm, the disadvantage of excessive adaptation in C4.5 has been improved so that classification results not only have much higher accuracy but also statistic meaning.
文摘2015年2月,美国大学与研究图书馆协会(ACRL)正式发布《高等教育信息素养框架》(Framework for Information Literacy for Higher Education)(以下简称《框架》)。它是国际范围内信息素养教育的重要指导性文件,发布后立即引起国际信息素养教育界的强烈反响,国内业界人士也纷纷对它的内容进行分析解读。本文对《框架》的理论基础与具体内容进行反思,认为《框架》的理论基础——"阈概念"与"元素养"并不完全契合信息素养教育实践,而且《框架》以学术研究而非信息素养为出发点,强调学术信息,弱化了学术信息以外的信息内容。除此之外,《框架》还忽视了信息过载的问题。
