The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) m... more The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) method for the determination of arsenic in cigarette tobacco samples is described. The method is relatively simple and has been shown to give values of total arsenic close to those obtained using methods requiring total dissolution and decomposition of all vegetable matter before analysis. Pre-treatment of samples slurried in nitric acid by ultrasonication permitted the extraction of about 90% of the total arsenic from tobacco samples. Further improvement in the recovery efficiency (up to 93-94%) was accomplished by the use of an additional step of short microwave-accelerated treatment. l-Cysteine was used as a pre-reduction agent. The accuracy and precision of the slurry sampling HGAAS method were studied using the certified reference material (CRM) CTA-OTL-1 Oriental Tobacco Leaves. Under the optimum conditions, as little as 2.6 ng of arsenic can be detected. The relative standard deviation of the overall procedure was calculated to be below 7.6% at arsenic concentration levels of 0.5-0.9 mg kg 21 and the analytical results obtained for the CRM agreed with the certified value. The main factors that influenced the reliability of the method were sample homogeneity, particle size and slurry concentration.
This study compared the effects of a constructivist-visual mind map teaching approach (CMA) and o... more This study compared the effects of a constructivist-visual mind map teaching approach (CMA) and of a traditional teaching approach (TTA) on (a) the quality and richness of students’ knowledge structures and (b) TTA and CMA students’ perceptions of the extent that a constructivist learning environment (CLE) was created in their classes. The sample of the study consisted of six classes (140 Form 3 students of 13–15 years old) selected from a typical coeducational school in Brunei. Three classes (40 boys and 30 girls) were taught using the TTA while three other classes (41 boys and 29 girls) used the CMA, enriched with PowerPoint presentations. After the interventions (lessons on magnetism), the students in both groups were asked to describe in writing their understanding of magnetism accrued from the lessons. Their written descriptions were analyzed using flow map analyses to assess their content knowledge and its organisation in memory as evidence of cognitive structure. The extent of CLE was measured using a published CLE survey. The results showed that the cognitive structures of the CMA students were more extensive, thematically organised and richer in interconnectedness of thoughts than those of TTA students. Moreover, CMA students also perceived their classroom learning environment to be more constructivist than their counterparts. It is, therefore, recommended that teachers consider using the CMA teaching technique to help students enrich their understanding, especially for more complex or abstract scientific content.
Science Education 76(4): 353-371 (1992) 0 1992 John Wiley & Sons, Inc. CCC oO36-8326/92/040353-19... more Science Education 76(4): 353-371 (1992) 0 1992 John Wiley & Sons, Inc. CCC oO36-8326/92/040353-19$M.oO 356 DHINDSA AND ANDERSON several learning predictive models, has accounted for the most learning variables although its predictive capacity is limited to fairly short-term learning experiences and where rate of communication is fairly constant. Moreover, major variables that influence information processing have been considered. Anderson (1983) tested his model by presenting descriptive information on Hydra and Good Health at a rate of 6.38 discourse units per minute (DUs/min) and reported that the model accurately predicted short-term information acquired by listening to a tape-recorded science lesson of 0-30 minutes. The communication rate of 6.38 DUs/min, while descriptive of an average rate observed in science classrooms, is not characteristic of all teacher discourse. Anderson (1971) reported a variation in communication rate from 6.34 DUs/min to 8.23 DUs/min in secondary school classroom science teaching. A number of researchers have reported a significant effect of communication rate on achievement (Spickerclaimed that increase in communication rate from 120 to 175 and from 125 to 175 words per minute (WPM), respectively, increased the achievement significantly, whereas a further increase in communication rate to 225 WPM decreased achievement significantly. A number of researchers have claimed that an increase in communication rate beyond 175 WPM produces a significant loss in achievement (Kussat). Data collected by Jester and Travers , and, Sticht and Glasnapp (1972) indicated that an increase in communication rate from 175 WPM to 375 WPM markedly affected information acquisition. It declined slowly during the initial stage of increased communication rate, then accelerated in decline and finally once again showed only a moderate decrease. The data also indicated that a stage is reached at which further increase in communication rate did not seem to affect achievement. The achievement curve became asymptotic to the rate axis. The communication rate has been identified as a learning variable, but it has not been modeled mathematically to predict learning. Based on the above cited research relating communication rate to achievement, additional improvements in this study have been made in predicting achievement based on communication rate. The mathematical modeling of communication rate will help us understand how communication rate influences learning and may help the teachers to more carefully consider classroom communication rate in planning instructions.
The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) m... more The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) method for the determination of arsenic in cigarette tobacco samples is described. The method is relatively simple and has been shown to give values of total arsenic close to those obtained using methods requiring total dissolution and decomposition of all vegetable matter before analysis. Pre-treatment of samples slurried in nitric acid by ultrasonication permitted the extraction of about 90% of the total arsenic from tobacco samples. Further improvement in the recovery efficiency (up to 93-94%) was accomplished by the use of an additional step of short microwave-accelerated treatment. l-Cysteine was used as a pre-reduction agent. The accuracy and precision of the slurry sampling HGAAS method were studied using the certified reference material (CRM) CTA-OTL-1 Oriental Tobacco Leaves. Under the optimum conditions, as little as 2.6 ng of arsenic can be detected. The relative standard deviation of the overall procedure was calculated to be below 7.6% at arsenic concentration levels of 0.5-0.9 mg kg 21 and the analytical results obtained for the CRM agreed with the certified value. The main factors that influenced the reliability of the method were sample homogeneity, particle size and slurry concentration.
This study, based on constructivist learning theory, examined how effectively preservice chemistr... more This study, based on constructivist learning theory, examined how effectively preservice chemistry teachers (N = 43) can be educated to think flexibly and to reorganize their thinking in a way that may complement diverse ways students approach the subject domain. The teacher's cognitive structure was assessed prior to and after a conceptual change intervention using flow-map narrative analyses. There was a significant change in the organization of the preservice teacher's narrative after the conceptual change intervention, including greater networking of ideas and more thematic development of the content. Hence, a conceptual change approach may be a useful way to educate teachers to be more responsive to student individual differences when planning and delivering science lessons.
Abstract The aim of this study was to compare the effects of constructivist-informed, technology-... more Abstract The aim of this study was to compare the effects of constructivist-informed, technology-rich learning environments and traditional learning environments on students' achievement. The sub-jects of the study were 115 Form V combined science students (16 ...
A novel method for sample preparation by ultrasound-accelerated solid-liquid extraction prior to ... more A novel method for sample preparation by ultrasound-accelerated solid-liquid extraction prior to selenium determination in the phosphate-rich biological samples by electrothermal atomization atomic absorption spectrometry (ETAAS) with continuum-source background correction and nickel nitrate as a chemical modifier was established and compared with the results of conventional sample wet decomposition (however, this last item was not the object of this study). Diluted (4%) nitric acid was used as an extraction medium. The evaluation of the analytical results for biological Certified Reference Materials indicates that the results of a selenium determination after wet acid digestion (HNO3+HC1+H2O2) agreed well with the certified values, whereas the proposed solid-liquid extraction procedure can be used for simple and rapid control of the selenium levels.
The suitability of the single vessel principle (performing all steps of an analytical procedure i... more The suitability of the single vessel principle (performing all steps of an analytical procedure in one vessel) for cold vapour atomic absorption spectrometric determination of mercury in biological solids was evaluated. The single vessel method gave a lower mean blank level with better precision, hence lower detection limits, as compared to the conventional method. The determination of total mercury in biological standard reference materials by the single vessel method also produced significantly higher mercury values and better precision than the conventional method. However, the mercury concentrations obtained in certified reference materials by the use of both methods were close to the mean certified values. Moreover, the use of the single vessel method is cost effective, rapid and environment friendly. The use of the single vessel technique is therefore recommended for accurate and reliable determination of mercury in biological solids.
This experiment is commonly conducted in lower secondary classes to prove wrongly that air contai... more This experiment is commonly conducted in lower secondary classes to prove wrongly that air contains about 20% oxygen despite our knowledge that burning in a closed environment does not consume oxygen completely. The aim of this study was to evaluate (a) science teachers' conceptions associated with this experiment and (b) their confidence in the accuracy of their conceptions. Data were collected administering a multiple choice question test (MCQ) to, and by conducting interviews with, teachers. The MCQ test also asked them to record their confidence that their responses were correct. The teachers were shown to have many misconceptions about this experiment but they are highly confident that their conceptions are correct. For example, they reported that all oxygen in the jar is used up completely before the candle is put out. They also believed that water rose in the jar to take up empty space created by (a) used up oxygen or (b) dissolved carbon dioxide without considering molar ratio between oxygen and carbon dioxide during burning of carbon in oxygen (air) and the solubility rate of carbon dioxide in water. They are highly confident in these responses. It appears that conceptual knowledge stored in a teacher's brain is not properly connected, therefore they are unable to pool it together effectively to solve simple problems as described in this experiment. The study will also discuss some simple experiments that could help teachers to correct their misconceptions and improve the connectivity of concepts in their brains for effective teaching. Teachers in schools and teacher educators in teacher training institutions should target teaching for understanding. More research on how to make the teachers more flexible in thinking and in pooling their information to solve simple problems confidently and accurately is recommended.
- The aims of this study were to estimate the total amount of mercury released to the environment... more - The aims of this study were to estimate the total amount of mercury released to the environment during 60 years of gold mining (1867-1926) at Gympie, Queensland, Australia and to measure the mercury levels in soil samples surrounding the mining activity. We estimated that 1902 tonnes of mercury was released to the environment and about 1236 tonnes of which was released to the air. The mean mercury in the soil samples in the vicinity of the Scottish battery varied from 1.07 to 99.26 μg g-1 as compared to 0.075 μg g-1 as background mercury concentrations. The maximum mercury concentration measured in sediments of the Langton Gully was 6.12 μg g-1. These results show that large amount of mercury was used in this area during gold mining. Since mining is active in the area and Langton Gully flows into Mary River, we therefore, recommend that mercury concentration in air and fish should be monitored.
The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) m... more The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) method for the determination of arsenic in cigarette tobacco samples is described. The method is relatively simple and has been shown to give values of total arsenic close to those obtained using methods requiring total dissolution and decomposition of all vegetable matter before analysis. Pre-treatment of samples slurried in nitric acid by ultrasonication permitted the extraction of about 90% of the total arsenic from tobacco samples. Further improvement in the recovery efficiency (up to 93-94%) was accomplished by the use of an additional step of short microwave-accelerated treatment. l-Cysteine was used as a pre-reduction agent. The accuracy and precision of the slurry sampling HGAAS method were studied using the certified reference material (CRM) CTA-OTL-1 Oriental Tobacco Leaves. Under the optimum conditions, as little as 2.6 ng of arsenic can be detected. The relative standard deviation of the overall procedure was calculated to be below 7.6% at arsenic concentration levels of 0.5-0.9 mg kg 21 and the analytical results obtained for the CRM agreed with the certified value. The main factors that influenced the reliability of the method were sample homogeneity, particle size and slurry concentration.
This study compared the effects of a constructivist-visual mind map teaching approach (CMA) and o... more This study compared the effects of a constructivist-visual mind map teaching approach (CMA) and of a traditional teaching approach (TTA) on (a) the quality and richness of students’ knowledge structures and (b) TTA and CMA students’ perceptions of the extent that a constructivist learning environment (CLE) was created in their classes. The sample of the study consisted of six classes (140 Form 3 students of 13–15 years old) selected from a typical coeducational school in Brunei. Three classes (40 boys and 30 girls) were taught using the TTA while three other classes (41 boys and 29 girls) used the CMA, enriched with PowerPoint presentations. After the interventions (lessons on magnetism), the students in both groups were asked to describe in writing their understanding of magnetism accrued from the lessons. Their written descriptions were analyzed using flow map analyses to assess their content knowledge and its organisation in memory as evidence of cognitive structure. The extent of CLE was measured using a published CLE survey. The results showed that the cognitive structures of the CMA students were more extensive, thematically organised and richer in interconnectedness of thoughts than those of TTA students. Moreover, CMA students also perceived their classroom learning environment to be more constructivist than their counterparts. It is, therefore, recommended that teachers consider using the CMA teaching technique to help students enrich their understanding, especially for more complex or abstract scientific content.
Science Education 76(4): 353-371 (1992) 0 1992 John Wiley & Sons, Inc. CCC oO36-8326/92/040353-19... more Science Education 76(4): 353-371 (1992) 0 1992 John Wiley & Sons, Inc. CCC oO36-8326/92/040353-19$M.oO 356 DHINDSA AND ANDERSON several learning predictive models, has accounted for the most learning variables although its predictive capacity is limited to fairly short-term learning experiences and where rate of communication is fairly constant. Moreover, major variables that influence information processing have been considered. Anderson (1983) tested his model by presenting descriptive information on Hydra and Good Health at a rate of 6.38 discourse units per minute (DUs/min) and reported that the model accurately predicted short-term information acquired by listening to a tape-recorded science lesson of 0-30 minutes. The communication rate of 6.38 DUs/min, while descriptive of an average rate observed in science classrooms, is not characteristic of all teacher discourse. Anderson (1971) reported a variation in communication rate from 6.34 DUs/min to 8.23 DUs/min in secondary school classroom science teaching. A number of researchers have reported a significant effect of communication rate on achievement (Spickerclaimed that increase in communication rate from 120 to 175 and from 125 to 175 words per minute (WPM), respectively, increased the achievement significantly, whereas a further increase in communication rate to 225 WPM decreased achievement significantly. A number of researchers have claimed that an increase in communication rate beyond 175 WPM produces a significant loss in achievement (Kussat). Data collected by Jester and Travers , and, Sticht and Glasnapp (1972) indicated that an increase in communication rate from 175 WPM to 375 WPM markedly affected information acquisition. It declined slowly during the initial stage of increased communication rate, then accelerated in decline and finally once again showed only a moderate decrease. The data also indicated that a stage is reached at which further increase in communication rate did not seem to affect achievement. The achievement curve became asymptotic to the rate axis. The communication rate has been identified as a learning variable, but it has not been modeled mathematically to predict learning. Based on the above cited research relating communication rate to achievement, additional improvements in this study have been made in predicting achievement based on communication rate. The mathematical modeling of communication rate will help us understand how communication rate influences learning and may help the teachers to more carefully consider classroom communication rate in planning instructions.
The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) m... more The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) method for the determination of arsenic in cigarette tobacco samples is described. The method is relatively simple and has been shown to give values of total arsenic close to those obtained using methods requiring total dissolution and decomposition of all vegetable matter before analysis. Pre-treatment of samples slurried in nitric acid by ultrasonication permitted the extraction of about 90% of the total arsenic from tobacco samples. Further improvement in the recovery efficiency (up to 93-94%) was accomplished by the use of an additional step of short microwave-accelerated treatment. l-Cysteine was used as a pre-reduction agent. The accuracy and precision of the slurry sampling HGAAS method were studied using the certified reference material (CRM) CTA-OTL-1 Oriental Tobacco Leaves. Under the optimum conditions, as little as 2.6 ng of arsenic can be detected. The relative standard deviation of the overall procedure was calculated to be below 7.6% at arsenic concentration levels of 0.5-0.9 mg kg 21 and the analytical results obtained for the CRM agreed with the certified value. The main factors that influenced the reliability of the method were sample homogeneity, particle size and slurry concentration.
This study, based on constructivist learning theory, examined how effectively preservice chemistr... more This study, based on constructivist learning theory, examined how effectively preservice chemistry teachers (N = 43) can be educated to think flexibly and to reorganize their thinking in a way that may complement diverse ways students approach the subject domain. The teacher's cognitive structure was assessed prior to and after a conceptual change intervention using flow-map narrative analyses. There was a significant change in the organization of the preservice teacher's narrative after the conceptual change intervention, including greater networking of ideas and more thematic development of the content. Hence, a conceptual change approach may be a useful way to educate teachers to be more responsive to student individual differences when planning and delivering science lessons.
Abstract The aim of this study was to compare the effects of constructivist-informed, technology-... more Abstract The aim of this study was to compare the effects of constructivist-informed, technology-rich learning environments and traditional learning environments on students' achievement. The sub-jects of the study were 115 Form V combined science students (16 ...
A novel method for sample preparation by ultrasound-accelerated solid-liquid extraction prior to ... more A novel method for sample preparation by ultrasound-accelerated solid-liquid extraction prior to selenium determination in the phosphate-rich biological samples by electrothermal atomization atomic absorption spectrometry (ETAAS) with continuum-source background correction and nickel nitrate as a chemical modifier was established and compared with the results of conventional sample wet decomposition (however, this last item was not the object of this study). Diluted (4%) nitric acid was used as an extraction medium. The evaluation of the analytical results for biological Certified Reference Materials indicates that the results of a selenium determination after wet acid digestion (HNO3+HC1+H2O2) agreed well with the certified values, whereas the proposed solid-liquid extraction procedure can be used for simple and rapid control of the selenium levels.
The suitability of the single vessel principle (performing all steps of an analytical procedure i... more The suitability of the single vessel principle (performing all steps of an analytical procedure in one vessel) for cold vapour atomic absorption spectrometric determination of mercury in biological solids was evaluated. The single vessel method gave a lower mean blank level with better precision, hence lower detection limits, as compared to the conventional method. The determination of total mercury in biological standard reference materials by the single vessel method also produced significantly higher mercury values and better precision than the conventional method. However, the mercury concentrations obtained in certified reference materials by the use of both methods were close to the mean certified values. Moreover, the use of the single vessel method is cost effective, rapid and environment friendly. The use of the single vessel technique is therefore recommended for accurate and reliable determination of mercury in biological solids.
This experiment is commonly conducted in lower secondary classes to prove wrongly that air contai... more This experiment is commonly conducted in lower secondary classes to prove wrongly that air contains about 20% oxygen despite our knowledge that burning in a closed environment does not consume oxygen completely. The aim of this study was to evaluate (a) science teachers' conceptions associated with this experiment and (b) their confidence in the accuracy of their conceptions. Data were collected administering a multiple choice question test (MCQ) to, and by conducting interviews with, teachers. The MCQ test also asked them to record their confidence that their responses were correct. The teachers were shown to have many misconceptions about this experiment but they are highly confident that their conceptions are correct. For example, they reported that all oxygen in the jar is used up completely before the candle is put out. They also believed that water rose in the jar to take up empty space created by (a) used up oxygen or (b) dissolved carbon dioxide without considering molar ratio between oxygen and carbon dioxide during burning of carbon in oxygen (air) and the solubility rate of carbon dioxide in water. They are highly confident in these responses. It appears that conceptual knowledge stored in a teacher's brain is not properly connected, therefore they are unable to pool it together effectively to solve simple problems as described in this experiment. The study will also discuss some simple experiments that could help teachers to correct their misconceptions and improve the connectivity of concepts in their brains for effective teaching. Teachers in schools and teacher educators in teacher training institutions should target teaching for understanding. More research on how to make the teachers more flexible in thinking and in pooling their information to solve simple problems confidently and accurately is recommended.
- The aims of this study were to estimate the total amount of mercury released to the environment... more - The aims of this study were to estimate the total amount of mercury released to the environment during 60 years of gold mining (1867-1926) at Gympie, Queensland, Australia and to measure the mercury levels in soil samples surrounding the mining activity. We estimated that 1902 tonnes of mercury was released to the environment and about 1236 tonnes of which was released to the air. The mean mercury in the soil samples in the vicinity of the Scottish battery varied from 1.07 to 99.26 μg g-1 as compared to 0.075 μg g-1 as background mercury concentrations. The maximum mercury concentration measured in sediments of the Langton Gully was 6.12 μg g-1. These results show that large amount of mercury was used in this area during gold mining. Since mining is active in the area and Langton Gully flows into Mary River, we therefore, recommend that mercury concentration in air and fish should be monitored.
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