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
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？
