Search

Στην παρούσα έρευνα διερευνήθηκαν ποσοτικά και ποιοτικά οι δυσκολίες που αντιμετωπίζουν στη «Χημική Κινητική» οι μαθητές Λυκείου. Για την ποιοτική φάση της διερεύνησης σχεδιάστηκε ένα ερωτηματολόγιο αποτελούμενο από ερωτήσεις πολλαπλής επιλογής και ερωτήσεις σύντομης απάντησης αντικειμενικού τύπου, το οποίο αφού αξιολογήθηκε, διακινήθηκε σε 619 μαθητές, 27 Γενικών Λυκείων της χώρας. Η ποιοτική φάση της διερεύνησης είχε τη μορφή προσωπικής ημιδομημένης συνέντευξης και πραγματοποιήθηκε με 15 μαθητές. Επιπλέον αναλύθηκε και εξετάσθηκε με συγκεκριμένα κριτήρια ο τρόπος με τον οποίο η δομή και το περιεχόμενο του σχολικού βιβλίου προσεγγίζει τα γεγονότα και τις έννοιες της Χημικής Κινητικής. Τα αποτελέσματα της έρευνας δείχνουν ότι αρκετοί μαθητές αντιμετωπίζουν δυσκολίες να: • αναγνωρίσουν τις συμβάσεις των συμβολικών αναπαραστάσεων • εκτελέσουν τις μαθηματικές πράξεις που απαιτούνται • αναγνωρίσουν ή/και να κατανοήσουν το πλήθος των πληροφοριών που μεταφέρουν τα διαγράμματα και τις αφαιρέσεις τους • διακρίνουν κινητικές και θερμοδυναμικές έννοιες • περιγράψουν λεκτικά και να εξηγήσουν φαινόμενα, χρησιμοποιώντας κατάλληλους χημικούς όρους. Η εξέταση του σχολικού βιβλίου έδειξε ότι σε αρκετά σημεία η παρουσίαση του περιεχομένου από το κείμενο και τις εικόνες, δεν διευκολύνει την εννοιολογική κατανόηση και μπορεί να συμβάλει σε μηχανική μάθηση αντί μάθηση με κατανόηση, στην ανάπτυξη εναλλακτικών ιδεών και στην αποθάρρυνση των μαθητών να εκτιμήσουν, να αγαπήσουν και να αφιερώσουν χρόνο στη μελέτη της Χημείας, λόγω της ελλιπούς κατανόησης του περιεχομένου της. In this study we quantitatively and qualitatively investigated the learning difficulties that 11th grade Greek students encounter with "Chemical Kinetics". For the qualitative phase of the research a questionnaire consisting of multiple choice questions and short answer objective type questions was developed, following its evaluation, it was administered to 619 students, in 27 General high schools across the country. The qualitative phase of the research had the form of a personal semi-structured interview and was conducted with 15 students. Moreover, the way in which the structure and content of the textbook approach the facts and concepts of Chemical Kinetics were analyzed with specific criteria. Research results show that students face difficulties in: • recognizing the conventions of symbolic representations • performing the mathematical operations required • recognizing and / or understanding the plethora of information conveyed in diagrams as well as their abstractions • distinguishing between kinetic and thermodynamic concepts • verbally describing and explaining phenomena using appropriate chemical terms. Textbook analysis indicated that its presentation at several points does not facilitate the conceptual understanding of the subject matter, and can contribute, to rote instead of meaningful learning, development of alternative conceptions, and a lack of student motivation to appreciate, enjoy and devote time to the study of Chemistry, resulting from an incomplete understanding of its content.

In this study we present an analysis of how the structure and content of the Greek school textbook approach the concepts of chemical kinetics, and an investigation of the difficulties that 11th grade Greek students face regarding these concepts. Based on the structure and content of the Greek textbook, a tool was developed and applied to students in the form of test questions in order to investigate the difficulties that they encounter with concepts and facts of chemical kinetics. Our results indicate that the textbook presentation at several points does not take into consideration basic findings of chemistry education research, which could improve the understanding of the content, and that a large proportion of Greek students show low comprehension levels of the concepts and facts of chemical kinetics. Given the important role of the school textbook in the learning process, it seems that the structure and content of the textbook do not facilitate the conceptual understanding of the subject matter, and together with other factors contribute to the difficulties that students face regarding concepts in chemical kinetics.

In this study we present an analysis of how the structure and content of the Greek school textbook approach the concepts of chemical kinetics, and an investigation of the difficulties that 11th grade Greek students face regarding these concepts. Based on the structure and content of the Greek textbook, a tool was developed and applied to students in the form of test questions in order to investigate the difficulties that they encounter with concepts and facts of chemical kinetics. Our results indicate that the textbook presentation at several points does not take into consideration basic findings of chemistry education research, which could improve the understanding of the content, and that a large proportion of Greek students show low comprehension levels of the concepts and facts of chemical kinetics. Given the important role of the school textbook in the learning process, it seems that the structure and content of the textbook do not facilitate the conceptual understanding of the subject matter, and together with other factors contribute to the difficulties that students face regarding concepts in chemical kinetics.

Cassava contains little zinc, iron, and β-carotene, yet it is the primary staple crop of over 250 million Africans. This study used a 24-hour dietary recall to test the hypothesis that among healthy children aged 2–5 years in Nigeria and Kenya, cassava’s contribution to the childrens’ daily diets is inversely related to intakes of zinc, iron, and vitamin A. Dietary and demographic data and anthropometric measurements were collected from 449 Kenyan and 793 Nigerian children. Among Kenyan children 89% derived at least 25% of their dietary energy from cassava, while among the Nigerian children 31% derived at least 25% of energy from cassava. Spearman’s correlation coefficient between the fraction of dietary energy obtained from cassava and vitamin A intake was r = −0.15, P

Importance Few long-term data describe the natural history of hepatic hemangiomas. Because these lesions are frequently imaged repetitively on studies performed for other indications, health care professionals are commonly confronted with the problem of a growing hemangioma. Because the rate and magnitude of normal growth is not well characterized, it is difficult to recognize lesions growing at an abnormal rate, which may require further evaluation or intervention. Objectives To establish quantitatively the expected growth rate of hepatic hemangiomas and to define a measure of hemangioma growth that could be used clinically to help identify hemangiomas for which growth is more than expected. Design, Setting, and Participants Retrospective cohort study at an academic hospital tertiary referral center evaluating the growth rate of hepatic hemangiomas on cross-sectional imaging studies during a 10-year period (1997-2007). The mean (SD) follow-up time was 3.7 (1.9) years. The radiology information system was searched in a 10-year period for hemangioma . Patients with hepatic hemangiomas that were 1 cm or larger as seen on cross-sectional imaging (computed tomography or magnetic resonance imaging), and 1 year or more apart were selected. Images with the longest interval between studies were selected for further review. Each study was rereviewed for diagnostic confirmation and to ensure consistency in measurement technique. Lesions were remeasured in 3 dimensions, and volumes were calculated using 3-dimensional software. Main Outcomes and Measures Primary outcomes include the fraction of hepatic hemangiomas that demonstrated growth during long-term follow-up and the annual growth rate of those lesions. Results A total of 163 hemangiomas were identified in 123 patients. The mean (SD) initial size was 3.2 (3.1) cm. During follow-up, 39.3% of hemangiomas grew 5% or more in mean linear dimension. The mean (SD) annual linear growth rate was 0.03 (0.21) cm for all lesions and 0.19 (0.23) cm for those that grew 5% or more. By volume, 44.7% of lesions grew 5% or more. The mean (SD) annual volumetric growth rate was 2.8% (21.0%) for all lesions and 17.7% (22.8%) in those that grew 5% or more. The initial size predicted the growth in linear dimension and volume ( P R = 0.00843; P = .92). Conclusions and Relevance Nearly 40% of hepatic hemangiomas grow over time. Although the overall rate of growth is slow, hemangiomas that exhibit growth do so at a modest rate (2 mm/y in linear dimension and 17.4% per year in volume). Further research is needed to determine how patients with more rapidly growing hemangiomas should be treated.