bluuebunny/crossref_metadata_2025 huggingface dataset:
On design of a robust decentralized controller for an interconnected multi-area power system with FACTS devices
Authors: Haroun Ali Hamid Gomaa
Published: June 2021

In this article, a robust active disturbance rejection control (ADRC) is proposed for load frequency control (LFC) of an interconnected multi-area power system. Two widely employed test systems, namely, two-areas and four-areas hydro-thermal power utilities are concerned to validate the efficacy of the suggested method. To enhance the performance of the system, series flexible ac transmission system (FACTS) like thyristor controlled series compensator (TCSC) and thyristor controlled phase shifter (TCPS) are considered. The simulation results indicated that the system performance is improved with the inclusion of FACTS devices. The adjustable parameters of the proposed FACTS controllers are optimized using particle swarm optimization (PSO) algorithm employing an Integral of Time multiplied Absolute Error (ITAE) criterion. The investigations showed  that the proposed controller provides better dynamic performance than others from the point of view of settling time, peak over/undershoot. Finally, the sensitivity analysis of the system is inspected by varying the system parameters and operating load conditions from their pre-specified values. It is observed that the suggested controller based optimization algorithm is robust and performs satisfactorily with the variations in operating load conditions, system parameters and load patterns.
Modelling of Compressive Membrane Action for Fully-laterally Restrained Two-way R.C Slabs
Authors: Ahmed Mohammed Wagieallah Rammah , Tagelsir Mustafa Abdelsalam Mohammed
Published: June 2021

Current design codes do not account for the effect of compressive membrane action (CMA) in reinforced concrete slabs, which can increase their capacities, and hence yields more economical design. This paper studies the influence of CMA for laterally restrained two-way slabs. The main aim is to develop a simple model to reasonably predict the enhancement in load-carrying capacity due to CMA for laterally restraint two-way RC slabs under uniformly distributed loading. In order to meet this aim, a numerical technique was used. The developed model had been validated against relevant experimental studies from literature. The parameters influencing the CMA were identified. These included the reinforcement ratio and span-thickness ratio. It was shown that the CMA decreases by increasing the percentage of reinforcement and span-to-thickness ratio. After that, a numerical model for evaluating the CMA for laterally restrained two-way slabs has been proposed. The model was examined against 43 slab specimens from literature. The correlation achieved was satisfactory, despite the wide range of variables involved in tests. The mean ratio of the experimental to the predicted ultimate load was 1.00, and the coefficient of variance (COV) equal to 25%.
تأثير الحرارة العالية على العارضات الخرسانية المسلحة المحسنة
Authors: عارف الأطرش منير , عارف الأطرش زكائي , عبشي مطيع , بدور إلهام , محمد عبد الماجد عصام
Published: June 2021

This research examined the effect of high temperatures on reinforced concrete beams made from the groundworks of Hassia region in Syria. Concrete received additions of silica ash and plasticizers. Concrete cubic samples were then prepared with dimensions (15*15*15 cm), and samples for beams with simple support on both sides, with fixed dimensions for all samples of (b*h* L = 18*25*150 cm, respectively), and with a covering thickness of 3 cm. These samples were heated at the age of 28 days to different temperatures in all aspects using an electric oven, which was specially manufactured for this research. Samples were then cooled according to two cooling methods. The first is rapid cooling with water, and the second is a slow cooling with air. Then, necessary laboratory experiments were performed on these samples to measure the percentage of change in resistance, and the change of the torque resistance value in the samples of beams. The samples of beams were modeled and studied according to the finite element method, using the ABAQUS program. The results were read and compared with the experimental results. The results showed a decrease in the value of the resistive torque for the samples of beams with an increase in the heating temperature. The value of this decrease reached about 70% of the value of the resistive torque at the normal temperature. A difference in the value of this decrease is observed at the same temperature in accord with the used method of cooling. In air-cooled samples, it is greater than in water-cooled samples up to 750 °C. The decrease after this temperature in water-cooled samples becomes greater, noting the explosion of some samples heated up to 850 °C when cooled with water. Finally, the results and recommendations are indicated.
Strengthening of Burri box Girder Bridge by using External post Tensioning Technology (Sudan)
Authors: Elrayah Khalafala Eltyeb , A Talaat Ismail
Published: June 2021

Ageing, and increasing traffic loads, has become a major problem into today bridge industry. These bridges go deficiency in its Load Carrying Capacity from ageing, exhibited in excessive deformation which renders the bridge usage to an unacceptable level. These will either, impose traffic restriction, or upgrading the existing bridges to defy these adverse conditions. At Burri Bridge, after 33 years on operation, signs of ageing showed in the excessive deformation and the departure of the deformed shape of the super structure from the design profile, and travelling along the bridge was un-comfortable and difficult trip riding. The Objective was to explore the strengthening of the Burri Bridge by using external post tensioned tendons to mitigate the ageing effects and to elevate the capacity of the bridge. It was requisite to examine the bridge before the application of external tendons to insure the stresses in its past status will qualify it for repair. Hence, the present study contains the analysis of the Bridge superstructure in two stages. The first is done in its Past status, and the second when external tendons are added to boost its capacity and defy the effect of past load level, and a new standard load tested. The model was analyzed using Midas Civil software. The study includes the design of the anchor beams where the fresh external tendons are terminated. The study proved that, the capacity of the Bridge is increased by 4.6 %, and this is interpreted in the increase of the Ultimate Flexural Strength and the decrease of the deformation after adding these external tendons. Some of the Techniques implemented are presented.
Foundations, Design, and Dynamic Performance of Wind Turbines: Overview and Challenges in Sudan
Authors: Asim Hamza Ruba , Osman Abdelatif Amged
Published: June 2021

Sudan is one of the developing countries that suffers from a lack of electricity, where the national electrification rate is estimated at 38.5%. In order to solve this problem, it is possible to use renewable energy sources such as wind energy. Beside many aspects to be considered at the design of wind turbine foundations, more attention should be given to the geotechnical part. There are many types of foundations for wind turbines. The foundation must satisfy two design criteria: 1) It should be safe against bearing failure in soils under design loads and settlements during the life of the structure must not cause structural damage; 2) In addition to static loads, wind turbine foundations loads are extremely eccentrically and the loading is usually highly dynamic. Therefore, the selection of foundation type should consider these two criteria taking into account the nature and magnitude of these loads. This paper presents a review of different types of wind turbine foundations of focusing on on-shore wind turbine foundation types and the dynamic response of wind turbine. The paper also demonstrate experimentally the dynamic response of the wind turbines using wind tunnel facility test on a scaled model.
إستخدامات ومستقبل القضبان المركبة على صناعة التشييد بالسودان
Authors: حسين محمد علي علي , مصطفى الطاهر مها
Published: June 2021

The In the 1960s, composite materials began to spread. These are materials that are made up of two different materials or more, and each material gives its best properties to obtain a compound with distinctive characteristics, the first of which is a reinforcing material that can be in the form of fibers made of high-resistance materials (such as carbon or glass fibers, for example), and the second material is one of plastics or colloidal polymers (Matrix), which give the final product its required form and it is called the incubator, and the mechanical properties of the final product are different from those of any of its composites. Composite materials have spread tremendously during the short period of their life due to their excellent mechanical properties compared to their low weight, they have entered all engineering fields, although they were originally born in the world of aircraft and spacecraft industry, where light weight plays a major role in the selection of materials. All objects designed from composite materials are assumed to have long life, so the materials involved are non-dissolved. However, this feature has recently become undesirable due to the difficulty in disposing of compounding materials after their useful life. For these reasons, research has recently tended to arrive at green composite materials that are organic biodegradable so that they degrade in the soil after being buried, i.e. as living organisms after their death, or they are reusable after the end of their life. The paper presents the latest developments in three important areas related to composite materials. The first is in the manufacture of fiber-reinforced bars, the second in technical requirements and the precautions to be known, and the third in use and its future in the construction industry in Sudan.
Lime –Metakaolin Interaction
Authors: M. I El-Sharif , A. A Alyamani , A. A Mutasim
Published: June 2021

The standard mix ratio of lime: pozzolana specified by all standards is 1:2 by weight to produce lime pozzolan cement (LPC) with the minimum required strength of 4 MPa. This ratio may be affected by many factors such as the quality of lime and pozzolana, in adition to the quantity of amorphous silica in pozzolana. In this paper a local kaolin and lime were investigated for their chemical, physical, mineralogical, and thermal properties, using various techniques such as XRF, DTG/DSC, and XRD. The produced metakaolin (MK) and hydrated lime (CH) were first tested for their reactivity, then different ratios of 1:2, 1:3, and 1:4 (lime: metakaolin) were tested to determine the optimum mix ratio of (LPC). The chemical, physical, and mineralogical analysis of samples showed their congruent with standard specifications adopted. The chemical analysis results showed that the local kaolin has composition with a SiO2+Al2O3+Fe2O3 content of 79.96%. The reactivity of MK toward CH is found to be within the limitation of standards. The mortar samples, made with a binder of ground MK and CH, developed a 28 days compressive strengths of 4.9, 14, and 16 MPa, for 1:2, 1:3, and 1:4 (CH: MK ) respectively. These findings suggest that LPC can be produced with high compressive strength if an optimum lime to pozzolana ratio is achieved.
Utilization of Waste Glasses as Supplementary Cementitious Materials
Authors: Hummaida Ahmed Yousif , Ibrahim Mohamed , Soliman Duaa
Published: June 2021

Wastes of Glass are recognized as pozzolanic material. This study aims to investigate utilization of local glass wastes in Sudan as supplementary cementitious materials. Two glass wastes specimens having different colors are procured from a local source namely Sudanese Emirati Glass and Metal Company (SEGMAL). Then thy are ground to micro sizes producing two types of glass powders, clear white glass powder (W-GP) and colored glass powder (C-GP). The two Specimens are characterized using tests specified in American Society for Testing and Materials ASTM C311. These tests include chemical properties using X-ray Fluorescence (XRF), Loss on Ignition (LOI), Insoluble Residue (IR), also physical properties such as fineness, specific gravity, water requirement, and strength activity index (SAI). This study shows that at 7 days W-GP and C-GP produced SAI of 84% and 87% at 7-days respectively. These values are more than the 75% of SAI’s requirements of ASTM C618. Both specimens have outperformed the control OPC mix at 28 days by producing SAI of 108.68% and 123.82% for GP-W and GP-C respectively.
Effect of Casting Temperatures and Curing Methods on Concrete Properties
Authors: Nur Eldayem Fath Elrahman , Abaker Mohammed
Published: June 2021

This study concentrates on the effects of curing methods and casting temperatures on concrete properties in cases of fresh and solid states. The targeted strength of the concrete mix is 25 N/mm2. An experimental work was performed at the laboratory of the Faculty of Engineering, University of Khartoum. Initially the tests on the basic materials (cement, fine aggregate, coarse aggregate) used. The program was testing the strength of concrete for a number of 80 samples of three cubes and test for absorption of water for 16 samples. These samples were casted at temperatures of 15, 25, 35 and 50 c0 and cured with four different methods. Methods of curing used are immersing the samples in water, cured through the winding sample with Hessian and sprinkled water, winding samples with plastic sheets to prevent evaporation of water or loss of water from the sample and paint samples with doofagard. In addition some samples were uncured. The samples were broken in three days, seven days, 28 days and 56 days. In the water absorption tests the samples were casted at different temperatures and different methods of curing except a coating sample with doofagard because the sample cannot absorption water. Also the workability tests for the samples casted at temperatures 15, 25, 35 and 50 c0 were performed. The find out of these experimental works showed that: (1) the compressive strength of cement concrete specimens increased with the period of curing (2) curing of concrete by immersion in water results in a high compressive strength than the other methods of curing (3) The concrete will gain low compressive strength if it is not cured at all after casting (4) The best degree of casting temperatures is 15 and 25 c0 that resulted in a good workability and high compressive strength; on the other hand casting concrete at high temperature reduce workability of fresh concrete.
Does Self-Compacting Concrete Exert more Pressure on Formworks than Normal Vibrated Flowing Concrete?
Authors: Hummida Ahmed Yousif , Ibrahim Osama , Elbadawi Alaa , Abdalgadir Firouz , Ahmed Osman , Abdalhleem Eslam , Bushra Ibrahim , Bushra Dia-alhag
Published: June 2021

This paper investigates lateral pressure on formwork indirectly by measuring lateral deflection using an innovative device. This device is fabricated from Polyvinyl Chloride (PVC) cylindrical mold in a fashion allowing occurrence and measurement of lateral movement at different depths using dial gauges. The lateral deflections for different systems of filling materials including water, sand, self-compacting concrete (SCC), and flowing concrete. The flowing concrete is tested under two conditions, vibrated (NVC), and non-vibrated (NCno.V). The results show that the NVC produced the largest lateral deflection which attributed to the vibration pressure. The measured lateral deflection are ranked descending in the following order: NVC, Water, SCC, NCno.V and Sand.
Management of Delay Factors in Construction Projects in Sudan
Authors: Abdul Aziz Mohamed Sarah , Mohamed Ahmed Adam Osama
Published: June 2021

The research aimed to find out and analyze the main causes of delay in construction projects. Just as so how most things are; an unforeseen delay on a construction site is inevitable. The research was designed to identify the possible causes of delay at construction projects from the literature review and previous studies which there are over than thirty causes of delay were displayed, then these causes tested by the analyzing the data and information that were collected from clients, consultants and contractors, researcher conduct site visits to interpretation the causes of delay that emerged during the implementation of the project. The analysis of correspondences letters between project parties; contractor, client, and consultant lead to characterize investigate are project finance, design changes, fluctuation of prices and incomplete design. The research defines who is responsible and type of delay in addition to the discussion of effects, risks, and mitigating of delay. Finally the research concluded with Recommendations such as security funding for the project at the project preparation stage, the contractors should be classified according to the experience which commensurate with the size of the project, The application of value engineering to avoid in complete design problems , it’s also strongly recommended future researchers to focus on building construction projects in other parts of the country since this was limited only to the capital city Khartoum through the case study.
The role of foreign workers in improving the effectiveness and efficiency of strategic construction projects in Sudan
Authors: Mohamed Ahmed Adam Osama , JadAlla Alnazeer
Published: June 2021

This study aims to address the issue of the role of the foreign workers in the promotion of work in the strategic construction projects in Sudan (a case study Dam Complex of Upper Atbara Project). The importance of this study lies in addressing one of the most important topics that concern the policy makers and the individuals in charge for the construction projects in Sudan. It also identifies their advantages and disadvantages, and address and deal with the shortcomings. The research dealt with evaluating the role of foreign workers in improving work and finding solutions to develop and qualify local labor in an effort to achieve this the data was collected by designing a questionnaires were distributed to the employees in the Dam Complex of Upper Atbara Project, and then unload the data collected through the questionnaires using the program Statistical Package for Social Sciences (SPSS). The results of the analysis showed that foreign workers played a role in the development of work in construction projects by 82%, and the reason that hinders the development of the skills of the Sudanese workers was the lack of training by 74%. The respondents also saw that there is a deficiency in the laws that control the work between foreign companies and local workers by 50%.Where 38% of the respondents did not know about the Sudanese Labor Law. Based on these results, the proposed solutions were presented in order to improve the performance of the construction industry in Sudan.
الموجهات الإرشادية لإعداد الدراسات التفصيلية وتحديد خطوات تنفيذ المشاريع من أجــــل قيام مشاريع ناجحة من الفكرة الى التشغييل
Authors: A. Hassaan Abdel Karim , H. Abdelatti Tagelsir
Published: June 2021

This paper was prepared to introduce the importance of knowledge and awareness by adhering to international standards when establishing large economic projects (> 1.0 m $) through preparing a detailed feasibility study. This includes all stages of the project (from idea to operation) and identifies project outputs and indicators of success, in order to establish best projects and for the optimal use of public money, based on a comparison and clarification with some successful projects to benefit from their experience. In fact, most projects in the Sudan are not studied and implemented according to a disciplined professional hierarchy and international standards, which often leads to their failure. Therefore, defining this problem and describing the solution should be a professional duty, the greater of which is located in the economic, engineering, the administrative, and the executive sectors, but the opinion of the civil engineer still remains as a key factor from the idea to the operational (Rule of Thumb). To solve this problem, we proposed simple guidelines for establishing projects from the idea to the operating, benefiting from our experience with the Ministry of Finance and Economic Planning and the Islamic Development Bank, and guidelines from consultant homes and financing institutions in this regard. Finally, we think that our suggested guidelines can be used as basic platform for all those involved and those in charge of these projects, so that the Ministry of Finance and Economic Planning (the largest financier) can end up as binding directors (along the lines of purchase and contracting laws and regulations) to obtain the funding required to implement projects public financed with loans or grants by global or local funding agencies.
Effect of Pozzolana and Lime on Expansive Soil Properties
Authors: S. M. Hamza Omer , M. E. Zumrawi Magdi , E. M. Mohamed Awad
Published: June 2021

This study investigates the effect of pozzolana and quick lime as stabilizer materials on expansive soil properties. Disturbed soil sample was collected from Al-Qadarif city in east of Sudan. The basic properties, swelling and strength of the soil were measured. The soil shows very weak strength and very high swelling potential. Mineralogical analysis tests were conducted to the soil using XRD tests. The soil contains significant amount of montmorillonite mineral (86%). Laboratory tests were undertaken on soil stabilized with varying percentage of pozzolana only (0, 5, 10, 15, 20, and 30%) and combination of pozzolana with constant content of quick lime (5%). Compaction, California Bearing Ratio (CBR), free swell, swell present and swelling pressure tests were performed on natural and treated soil. The pozzolana was obtained from Jebal Meidob and the lime obtained from local kilns in Kassala. The results showed that the treatment of expansive soil by combination of pozzolana and quick lime reduced soil swelling coupled with significant increase on soil strength. While the use of pozzolana only has marginal effective. It could be concluded that stabilization of expansive soil by pozzolana-lime admixture is successful.
Mechanically Stabilized Earth with Steel Reinforcement
Authors: M. E. Zumrawi Magdi , B. B. Barakat Abubaker , M. I. Abdalla Idris , A. A. Altayeb Rabab
Published: June 2021

This paper presents the Mechanically Stabilized Earth (MSE) technique as a practical option for earth retaining wall structures. The literature pertaining soil reinforcement methods and their application in MSE walls were intensively reviewed. The present work focused on evaluating the performance of MSE walls with backfill soil reinforced by steel strips. Almolid square overpass bridge in Khartoum, which was constructed in 2015 with MSE walls as lateral support of the overpass ramps, was considered as case study. Based on field observations, the current status of the overpass bridge has proven that the use of MSE walls is successful and beneficial for sustainability of the overpass.
المعتقدات والمفاهيم الدينية وسلوك استخدام الطريق الآمن لما بعد الرقمنة المرورية
Authors: الطيب الباقر , بدور الهام , عبد الماجد عصام
Published: June 2021

: النهضة العمرانية والطفرة السكنية والزيادة السكانية في المدن - عبر ربوع البلاد - واكبتها توسعة في البنى التحتية، وتزايد في توسيع الطرق، واطراد في بناء الكباري والجسور، مع التزايد المتنامي في أعداد المركبات الخاصة والعامة. الأمر الذي فاقم من حوادث الطرق والمرور، بسبب عدة عوامل من بينها سلوك مستخدم الطريق الآمن. ومن بين المؤثرات المعتقدات العقائدية، والمسلمات القدرية، والمشاعر الوجدانية، ربما بتداخل مع القيم الاجتماعية، والمفردات الثقافية، مما قد يعوق من تعزيز السلامة على الطريق. خاصة ان تداخلت هذه مع السلوكيات المعززة للصحة العمومية، ومعينات الوقاية من الإصابات، ومتطلبات منع الحوادث، ومستلزمات تأمين أخطار الطريق ومفاجآته. من ثم تعلق هذا البحث بالنظر في مؤشرات الأداء الرئيسة (لاستكشاف الارتباطات العقائدية والقدرية والمفاهيم الدينية، مع الاستخدام المتغير للطريق) على كل من صانع القرار (السياسي)، ومخطط الطريق ومصممه (المهندس ومخطط البلدية والمدينة)، ومستخدم الطريق (السائق)، والمرشد (الديني والاجتماعي والثقافي)، ومسؤول الأمن (الشرطة والمرور)، والقانوني (الجهاز العدلي والقاضي والمحامي). ومدى تأثير هذه المؤشرات على سلامة الطريق وأمنه، والتوعية المرورية الهندسية، لإرسال الرسائل المجتمعية، وترسيخ المفاهيم الهندسية المواكبة للحداثة والتقدم والرقمنة المرورية.
Can large-scale land acquisition deals improve livelihoods and lift people out of poverty in Sub-Saharan Africa? Empirical evidence from Tanzania
Authors: Nkansah-Dwamena Ernest
Published: June 2021

The recent wave of large-scale land acquisitions or land deals, popularly called ‘land grabbing’ in subSaharan Africa, has provoked vigorous debate over the potential benefits and risks to local people, with results structured by complex policy and institu­tional context. Land deals present new develop­ment challenges and aggravate old vulnera­bilities, raising critical questions for investigation. Yet empirical evidence of impacts on local populations is limited, particularly regarding how land deals affect local people’s livelihood assets, strategies, and outcomes. Guided by the sustainable livelihood approach and a quasi-experimental design, I compare livelihoods before and after a land deal project and between an affected and a control community in southwestern Tanzania. I use household surveys, focused group discussions, and key informant interviews to collect data. The ANOVA analyses revealed that the project severely deterio­rated households’ natural, financial, and social capital and had far-reaching impacts on well-being in the affected community compared to the control village. The study recommends that African countries should consider (1) scrutinizing land deals and enforcing contracts, (2) conducting rigorous envi­ron­mental and social impact assess­ment, (3) strengthening customary land rights and reinforc­ing compensation policies, and (4) mean­ingfully involving locals in land deal negotiations. This contribution responds to the deficit in research on land deals’ impacts on livelihoods and well-being and lays the groundwork for future research.
Los problemas de lápiz y papel en la formación de profesores
Authors: Martínez Losada Cristina , García Barros Susana , Mondelo Alonso Matilde , Vega Marcote Pedro
Published: June 2021

In this article a didactic approach for both initial and ongoing teacher training is presented, oriented towards the teaching and learning of paper and pencil problem-solving. Taking as a starting point teachers’ ideas of the educational possibilities of the problems which are generally used in Science classes (objectives reached and specific procedures which they develop), it then goes on to analyse and evaluate concrete traditional and innovative problem-solving models. This study will also look at commentaries and results regarding the development of these activities from both in-service and trainee teachers. It is shown that these teachers initially accept the educational interest of such problems, and they consider the innovative model to be the most useful because, apart from motivating the students, it also develops research procedures which the traditional problems ignore, and which are fundamental in scientific training.
El quehacer científico versus el quehacer áulico. Buscando rasgos del quehacer científico en libros de texto
Authors: Islas Stella Maris , Guridi Verónica Marcela
Published: June 2021

Here we outline a search for features of the scientific tasks in the paper-and-pencil and experimental activities proposed in the textbooks mostly used in Tandil. The topics selected were electric current, direct current circuits and electrical current effects. Among other results, it is worth nothing the notable variability found concerning the link between model and reality. There are also some reflections on the lack of emphasis in the conceptual analysis, on the possibility of diversifying the ways for the solution and the discussion on the relevance of mathematical expressions and numerical values.
Las redes conceptuales como instrumento para evaluar el nivel de aprendizaje conceptual de los alumnos. Un ejemplo para el tema de dinámica
Authors: Ciliberti N. , Galagovsky Lydia R.
Published: June 2021

Since the first articles concerning Concept Mapping many more have been reported looking for instruments to evaluate the level of student’s meaningful learning.In the present work we show that the construction of nuclear sentences for Concept Nets (Galagovsky, 1993a, b, 1996; Galagovsky and Ciliberti, 1994) demands high level of semantic analysis, which seems to help in inducing conceptual change. Results suggest that this type of class experience may help teachers to get complementary information about his/her student’s meaningful learning level.
Delimitando el campo de aplicación del cambio conceptual
Authors: Marín Martínez Nicolás
Published: June 2021

The teaching proposal based on conceptual change is, no doubt, the most spreaded one in Science Education; however, there is evidence from the teaching practice, as well as some theoretical considerations about students’cognitive conflicts, which, in the best case, limit the range of application of this proposal.
Criterios que utilizan los alumnos universitarios de primer ciclo para definir ser vivo
Authors: Mondelo Alonso Matilde , Martínez Losada Cristina , García Barros Susana
Published: June 2021

In our work we have tried to find out to what extent university students in their first three courses apply those criteria defining «the living things» concept. We have verified that they focus their attention on physiological aspects especially perceptible and macroscopic ones rather than on universal and microscopic characteristics.
La medida de las actitudes usando las técnicas de Likert y de diferencial semántico
Authors: Espinosa García J. , Román Galán T.
Published: June 2021

We have established a comparison between two popular methods to assess the attitude toward experimental sciences: The summated rating method, generally known as the Likert scale; and the semantic differential method. This study is carried out with university students of chemistry and high school students, finding that both attitude measuring techniques are equally suitable in our educative system. Moreover, the sex variable is not significant.
La valoración de argumentaciones y explicaciones : promover estrategias de retroalimentación
Authors: Duschl R. A.
Published: June 2021

This paper suggest focusing curriculum instruction and assessment models on the epistemic goals coupled with concept and performance goals. It discusses the design of learning environments that support students «doing science», in particular the role of assessment and the promotion of students development and evaluation of scientific claims.
Estudio de propuestas alternativas en la enseñanza de la termodinámica básica
Authors: Martínez J. M. , Pérez B. A.
Published: June 2021

We report in this work a research on an approach to Basic Thermodynamics teaching at secondary level. The results of four grups of students in different cities are discussed from qualitative and global quantitative perspectives in a complementary way. We suggest, in the light of the real implementation of that curricular proposal, some didactic recommendations for better adequacy to different contexts.
Resolver el problema abierto: Teñir lanas a partir de productos colorantes naturales. Una actividad investigativa para la enseñanza secundaria obligatoria
Authors: Martínez Aznar M. Mercedes , Ovejero Morcillo P.
Published: June 2021

We present in this paper a class work for solving investigative problems, inserted into the theoretical constructivist context. We have chosen the topic «Dye wool with natural dyers», for its relevance in Organic Chemistry and also for its cultural and social interest, showing an actual perspective of Science.On the other hand, we develop the class performance with emphasis in assessment.
Aprendizaje y enseñanza del contraste de hipótesis: concepciones y errores
Authors: Vallecillos A. , Batanero Bernabeu Carmen
Published: June 2021

In spite of the numerous references to problems derived from the incorrect use of the statistical tests or from misinterpretations of their results by experimental researchers in different areas, the educational world has stayed until the moment detached from them. In this paper we present the results of a wide research aiming at carring out a comprehensive evaluation of the learning of the hypothesis test by undergraduates. We point to some difficulties and errors that might underlie the origin of the denounced problems and that the teaching will have to take into account for an improvement of the learning of the topic. Likewise, we describe students’ conceptions about two key concepts in statistical test: the logical structure of hypothesis testing and the level of significance.
Delimitación de "lo que el alumno sabe" a partir de objetivos y modelos de enseñanza
Authors: Marín Martínez Nicolás , Jiménez Gómez Emma , Benarroch Benarroch Alicia
Published: June 2021

The educational principle proposed by Ausubel; «to find out the knowledge of the pupil and teach him consequently» is assumed by most of the educators; however, this principle does not delimit the sentence: «the knowledge of the pupil». So this sentence can have different interpretations according to the information the teacher requests from the pupil's cognitive structure to carry out the instructional process that, at the same time, depends on the teaching objetives. From here, in this paper we attempt to delimit «the knowledge of the pupil» about science as useful information to carry out the design of teaching based on the Altenative Conception Movement, Ausubel's Theory and Piaget's Theory.
Escuchando el sonido: concepciones sobre acústica en alumnos de distintos niveles educativos
Authors: Perales Palacios F. Javier
Published: June 2021

In recent years, many articles have been published on students' preconceptions of different theoretical concepts in Physics. Howewer, one area of this discipline which has received very little attention is that of Acoustics. This article first examines Acoustics from a wide range of perspectives, placing it within a scientific, didactic, and sociological framework. Secondly, it analyzes the results of a test given to students of different ages and levels in order to identify common preconceptions of Acoustics. Finally a reflection about the possible implications these might have for the Physics classroom is made.
Deficiencias epistemológicas en la enseñanza habitual de los conceptos de campo y potencial eléctrico
Authors: Furió-Mas Carles , Guisasola Aranzabal Jenaro
Published: June 2021

This article intends to analyse up to what extent the scarce learning produced when introducing the basic concepts on electrostatics is due to deficiencies and inadequacies in its routine teaching. So, on the one hand, we analyse what have been the principal epistemological leaps forward in the making of electricity as a science. On the other hand, we analyse Physics books and the teachers’ opinions.
Una propuesta: enseñar física a niños de grados elementales
Authors: Barbosa Lima M. C. , Alves L. , Gonçalvez Ledo R. A.
Published: June 2021

With the purpose of doing a previous presentation on Physics issues to children in their school initial steps, we intend to discuss a proposition using the scope of some tales as an appropriate tool to reach that objective.Our paper deals with two experiences. We have presented and established some comments in two of our municipality of Rio de Janeiro schools. In one of them, a public school which deals with students of a lower economic class and another one, a private school dealing with students of a middle economic class.In order to assist actively in the process of Physics teaching, as a sequence of our proposition, we are describing one of our experiences, which is being developed with educators responsible for students of these levels.
Hipótesis, citas, resultados: reflexiones sobre la comunicación científica en didáctica de ciencias
Authors: Jiménez Aleixandre María Pilar , García-Rodeja I.
Published: June 2021

This paper raises a reflection on the role of scholarly papers in the dissemination of research in Science Education, and in the discussion about educational theories. The convenience of a rigorous distinction in each paper between what are hypotheses or opinions, what are evidences, experimentally tested, and what constitutes a metanalysis from literature review, is suggested. These suggestions attempt to improve the quality of scientific communication in the community doing research in Science Education.
Concepciones de los profesores sobre la enseñanza de las ecuaciones diferenciales a estudiantes de química y biología. Estudio de casos
Authors: Moreno M. , Azcárate Carmen
Published: June 2021

Intending to quest about the conceptions math teachers hold about how to teach Differential Equations to chemistry and biology students, we have devised a research tool which allows us to derive relevant information. We use different means to collect the adequate data related to the qualitative research, targeting the exploration of what teachers «say they do» and what «they do and would like to do». The use of concept maps and a questionnaire, along with a recorded interview, has revealed itself as an accurate means for the appropriate analysis of data, as shown in the case study we hereby include.
Los suelos en la enseñanza de la teoría ácido-base de Lewis. Una estrategia didáctica de aprendizaje por investigación
Authors: Salcedo Torres L. E. , García García José Joaquín
Published: June 2021

This article describes and analyses the results obtained in a didactical experimental strategy, structured in the Teaching and Learning model which is based on research.The students are involved in situations, where problems related with the soil are used in order to help the significative construction of the acid and base’s concepts related to the Lewis’ Theory in order to increase the students mental ability for analysing and synthesizing and also to develop their attitudes towards science.
Qué piensan los profesores de cómo se debe enseñar
Authors: Fernández González J. , Elortegui N.
Published: June 2021

Authors propose different types of teacher after working with a group of Primary and Secondary teachers in the Science area. In a structuralistic way, differentiating elements were determinated and «behaviour models in teaching/learning tasks» were established with the intention of expliciting theories behind each practice and, therefore, opening the way to its analysis and evolution.
El principio de Le Chatelier a través de la historia y su formulación didáctica en la enseñanza del equilibrio químico
Authors: Quílez Pardo J. , Sanjosé López V.
Published: June 2021

The historical evolution of the Le Chatelier’s principle is connected with its use in the chemistry classroom. The apparent simplicity in which the Le Chatelier’s principle was first formulated and the success achieved in the implementation of some important industrial processes gave it an initial acknowledgement still kept nowadays. Nevertheless, since the beginning of this century, different authors have pointed out the limited character of the qualitative rule and its vague and ambiguous formulation. Furthermore, thermodynamics gives for the Le Chatelier’s principle some quantitative formulations that limit its applicability. However, most general chemistry textbooks have treated the Le Chatelier’s qualitative rule as a universal and infallible principle, making suitable for teaching the statement given by Le Chateiierin 1888. This didactic teaching approach is a source of different misconceptions which are generated in the prediction of the evolution of a perturbed chemical equilibrium system. Hence, some authors have suggested avoiding the Le Chatelier’s rule. This new option assumes to use exclusively the chemical equilibrium constant.
La orientación de las prácticas de laboratorio como investigación: un ejemplo ilustrativo
Authors: Gil Pérez D. , Valdés Castro Pablo
Published: June 2021

This paper offers a detailed example of transformation of a science practical work, from the usual simple recipe into an open problematic situation capable of favouring pupils’ research.
Análisis de las actuaciones de los alumnos de 3· de BUP en la resolución de problemas que comparan áreas de figuras geométricas
Authors: Cobo Lozano P.
Published: June 2021

This paper is a case study which intends to analyze and compare the performance of two pairs of 3rd BUP students when solving two mathematics problems in which the areas of geometric figures are related. The analysis and comparison of the performance of both pairs has been conducted from a two-fold perspective, the knowledge that students use during the problem-solving process, and the control they show over this process. For this, the protocol analysis technique has been used, by means of video recordings of the problem-solving processes.
Algunas contribuciones de la mujer a las ciencias experimentales
Authors: Muñoz-Páez A.
Published: June 2021

Contributions of women to Science in the past have been scarce, but relevant in several cultures. Nevertheless, these contributions have been further obscured by subsequent male writers. Even in recent publications there is a strong tendency to neglect the role of women in Science. A few examples are given to show that there were a few outstanding female scientist in Antiquity, such as Hypatia of Alexandria and Miriam the Jewess that contradict the baconian view of science, which creates a dichotomy between feminine and scientific stereotypes. A small summary of the achievements of these two scientists as well as of a few others is presented. In modern times, most part of the research wasdeveloped within the framework of Universities and, since women were not admitted until theend of last century, they disappeared of the scientific world. Once they were admitted in Universities, their contribution to Science increased, but strong differences are found depending upon the country. Thus, while in Spain they are now reaching medium levels, in the United States there has been a very productive female scientific community since the end of last century.
Un curso de actualización y cambios conceptuales en profesores de física
Authors: Pacca Jesuïna Lopes de Almeida , Pacca A. , Villani Alberto
Published: June 2021

The behaviour of secondary school Physics teachers atari updating course was analysed; the results led to an indication of a conceptual change in their practice. The object of analysis and discussion was the actual pedagogical planning by the teacher. The dynamics developed in the course favoured the reelaboration of the teacher’s conceptions, not only in relation to Physics contents but also in relation to the students’ learning process; a conceptual change in three sequent phases could be characterized.
Ciencia y teoría curricular
Authors: Darós W. R.
Published: June 2021

The purpose of this study is to pay attention to the structure of scientific thinking as a means to form the curriculum. Therefore an analogic concept of science is analysed in order to be useful to different kinds of knowledge and academic matters.This study implies that science thought begins in everyday's thought perfected. In this way science is a powerful tool to develop the human will and moral conduct of a person. The scientific thought is particularly efficient for a didactic theory to balance the psychological aspect of mind in the students with the logic and objective demands.
Validación de un test para verificar si el alumno posee concepciones científicas sobre calor, temperatura y energía interna
Authors: Lang da Silveira F. , Moreira Marco Antonio
Published: June 2021

This study is a continuation of the task of validating a paper and pencil test to check whether the student has scientific conceptions about heat, temperature and internal energy in which we are working since 1989. The third version of this instrument is presented here. Previous versions (Silveira, Moreira and Axt, 1990,1991) were modified after an analysis of internal consistency carried out with additional data provided by 168 students of introductory physics at UFRGS. The present version is constituted by 23 items, which might be divided into three groups, each one corresponding to one of the three concepts: heat, temperature and internal energy. This division is based on a logical content analysis as well as on an empirical analysis of students’ responses.
La didáctica de la genética: revisión bibliográfica
Authors: Bugallo Rodríguez A.
Published: June 2021

The aim of this paper is to partially review the historic development and present situation of Genetics Education. Three areas will be examined: 1) Those studies which analyse the significance of the subject, as well as the problems which result from it. 2) How research in this field has been affected by the controversia] move to include the subject in the curriculum for the Secondary Education. 3) The growing interest in the studies on Genetics problem solving, and its relationship with the conceptual knowledge.
Concepciones iniciales sobre la asociación estadística
Authors: Estepa Castro José Antonio , Batanero Bernabeu Carmen
Published: June 2021

In this paper we make a summary of psychological investigation about statistics association. The results of experimental study about previous conceptions are shown. This study has comprised the students' judgments of association. Using factorial analysis, we have identified five factors, which determine the structure of students' strategies. We also show a qualitative study about students' strategies in 2 x 2 and r x c contingency tables, scatterplots, and comparison of a numerical variable in different samples. Finally we describe four different misconceptions about statistical association and the conclusions of this paper.
Planificación de una unidad didáctica: el estudio del movimiento
Authors: García García José Joaquín , Pro Bueno Antonio de , Saura Llamas Octavio
Published: June 2021

In this study we attempt to apply an outline of Teaching Units for the study of Cinematics at Secondary Level. Having analysed the teaching problems indicated by teachers, the scientific contents involved and the methodological problems, a sequence of learning contents is established from a creative construction perspective.
Secuencia de enseñanza sobre el electromagnetismo
Authors: Meneses Villagrá Jesús Ángel , Caballero Sahelices M. Concesa
Published: June 2021

In orden to plan the teaching sequence of any physical topic, weconsider essential to bear in mind three factors, at least: the scientific problems that arise from the subjects to be studied, the conceptions of the students to whom the teaching is addressed, and above all, the strategies and methodological process to be taken. This paper presents the didactic model, based on a constructivist approach, we use, the university students' conceptions about electromagnetism, the conceptual map where we make explicit our points of view of the concepts we work on, and the group activities we have designed in order to promote the conceptual, methodological and attitudinal change.
Estudio sobre el comportamiento visual en álgebra de los alumnos del segmento educativo 14-16
Authors: Meavilla Seguí Vicente
Published: June 2021

The visual characterisation in Algebra of a sample of pupils in the 14-16 age -group has been studied. In this paper we suggest, in the light of the results of the study, didactic recommendations for the exploitation of visual reasoning in the teaching of Algebra in schools.