Quasi-static axial compression behavior of empty and polystyrene foam filled aluminum tubes

Thesis (Master)--Izmir Institute of Technology, Mechanical Engineering, Izmir, 2003Includes bibliographical references (leaves: 82-86)Text in English; Abstract: Turkish and Englishxiv, 86 leavesThe strengthening effect of foam filling and the effect of foam filling on the crushing properties of the light weight foam filled circular tubes were investigated through the polystyrene foam filled thin-walled Al tubes of 16 and 25 mm in diameter. The empty tubes crushed progressively in asymmetric (diamond) mode. The foam filling however turned the deformation mode into progressive axisymmetric (concertina) mode in 25 mm Al tube, while the deformation mode in foam filled 16 mm Al tube remained to be the same with that of the empty tube. The strengthening coefficients of foam-filling defined as the ratio between the increase in the average crushing load of the filled tube with respect to empty tube and plateau load (load corresponding to the plateau stress of the foam) were found to be 1.8 and 3.2 for the concertina and diamond mode of deformation, respectively. The higher value of strengthening in diamond mode of deformation was attributed to the filler deformation beyond the densification region. This was also confirmed by the microscopic observation of the partially crushed sections of the filled tubes. The interaction effect between tube and filler was assessed by the compression testing of the partially foam filled tubes. The effects of filler density, deformation rate (in the range between 0.001-0.04 s-1) and the use of adhesive between the tube wall and filler on the average crushing load, stroke efficiency and specific absorbed energy of the tubes were determined. The specific absorbed energy of the filled tube was compared with that of the empty tubes of wall thickening on the equal mass basis. Finally, two modes of deformation modes were proposed for the crushing behavior of the foam filled thin-walled Al tubes

Öğrencilerin hareket problemlerinin çözümünde kullandıkları stratejilerin problemin sunumuna göre incelenmesi

In this research, it was aimed to analyze the problem solving strategies used during solving problems related to constant speed and constant acceleration motion, which are often used in graphs, according to the presentation of the problem (text and graph). The research was carried out with 119 students studying in the 11th grade. In the research conducted in a case study pattern, data were collected using the problem solving strategies scale used in Physics at the high school level and open-ended questions about problems presented in two different ways. Scores from the scale were analyzed through the SPSS 25 program, and data from open-ended questions were analyzed by content analysis. According to the results obtained from the scales, it was determined that the problemsolving strategies used by students did not differ according to the presentation of the problem, but there was a difference in the stages of understanding the problem and organizing the problem according to the results obtained from open-ended questions. According to these results, it can be said that the way the problem is presented mostly affects the stage of understanding the problem. The understanding phase affects the solution process and the time required for the solution. Therefore, different techniques can be used to understand the problem according to the presentation of the problem during teaching.Bu araştırmada grafiklerden sıklıkla faydalanılan sabit hızlı ve sabit ivmeli harekete ilişkin problemlerin çözümü sırasında kullanılan problem çözme stratejilerinin problemin sunumuna (metin ve grafik) göre incelenmesi amaçlanmıştır. Araştırma 11. sınıfta öğrenim görmekte olan 119 öğrenci ile yürütülmüştür. Bir durum çalışması deseninde yürütülen araştırmada Lise Düzeyinde Fizikte Kullanılan Problem Çözme Stratejileri Ölçeği ve iki farklı şekilde sunulan problemlere ilişkin açık uçlu sorularla veriler toplanmıştır. Ölçekten alınan puanlar SPSS 25 programı aracılığı ile analiz edilerek, açık uçlu sorulardan elde edilen veriler ise içerik analizine tabi tutularak bulgulara ulaşılmıştır. Ölçeklerden elde edilen bulgulara göre öğrencilerin kullandıkları problem çözme stratejilerinin problemin sunumuna göre farklılaşmadığı, ancak açık uçlu sorulardan elde edilen bulgulara göre problemi anlama ve problemi örgütleme aşamalarında farklılık olduğu belirlenmiştir. Bu sonuçlara göre problemin sunum şeklinin en çok problemi anlama aşamasını etkilediği söylenebilir. Öğrencilerin en fazla problemi anlama aşamasına yönelik stratejileri kullandıkları tespit etilmiştir. Anlama aşaması çözüm sürecini ve çözüm için gereken süreyi etkilemektedir. Bu nedenle öğretim sırasında problemin sunumuna göre problemi anlamaya yönelik farklı teknikler kullanılabilir

Optimization of the axial crushing behavior of closed-cell aluminum foam filled welded 1050 al square-cross section crashboxes

Thesis (Master)--Izmir Institute of Technology, Mechanical Engineering, Izmir, 2009Includes bibliographical references (leaves: 194-209)Text in English; abstract: Turkish and Englishxx, 211 leavesThe crushing behavior of partially Al closed-cell foam (Alulight AlSi10) filled 1050H14 Al crash boxes was investigated at quasi-static and dynamic deformation velocities. The quasi-static crushing of empty and filled boxes was further simulated using LS-DYNA. Finally, the crushing of partially foam filled 1050H14 crash boxes was optimized using the response surface methodology. The used optimization methodology was also applied to the boxes made of a stronger Al alloy, 6061T4 Al, and filled with a higher strength Al foam, Hydro Al closed cell foam, in order to clarify the effect of box material and foam filler strength on the crushing behavior of the filled boxes. Within the investigated tube thickness and foam relative density range, the energy absorption of 1050H14 boxes was optimized at 3 mm wall thickness and 0.1114 (Alulight) and 0.0508 (Hydro foam) foam filler relative density. The increase in specific energy absorption of 1050H14 crash box was 5.6% with Alulight and 21.9% for Hydro foam filling. The SEA values of empty, partially and fully foam filled boxes were predicted as function of box wall thickness between 1 and 3 mm and foam filler relative density between 0 and 0.2, using the analytical equations developed for the mean crushing loads. The analysis indicated that both fully and partially foam filled boxes were energetically more efficient than empty boxes above a critical foam filler relative density. Partial foam filling however decreased the critical foam filler density at increasing box wall thicknesses

Measuring the marketing performances of state forest enterprises in Turkey

Today, any enterprise has to consider marketing as important as production. Production and marketing are two complementary activities in enterprises. The increase in marketing effectiveness is achieved through measuring the activity outcomes that can be described as marketing performance. Because marketing is a social science and, therefore, determining the marketing performance system concretely, examining it and determining its principles may not be possible, a need for a new model was felt to represent the real system, and, consequently, a multi dimensional purpose-system model was developed. This model was applied in the eighty-nine state forest enterprises in Turkey which arebranches of the General Directorate of Forestry and which are run on the principles of business enterprise. This study covers a limited period of time (1999 - 2003), and 41 variables were developed in order to measure the marketing performances of these enterprises. As a result of the statisticalanalyses, the total production area (TPA), total production costs (TPC), total number of the personnel working in the management unit (TNPWM), total growing stock (TGS), total investment amount (TIA), number of the assistant personnel separated from the management unit (NAPSM), distance to city center (DCC), total marketing/sale expenditure (TME), total management unit area (TMUA), total sales (TS), total forest area (TFA), total personnel expenditures (TPE), total production amount (TPAM) andtotal market priced product income (TMPPI) were found to be the most important marketing variables in the state forest enterprises. It was also found that the marketing performance could be explained 77.328% with the 14 variables that were used in this model

Shake Table Tests to Measure the Dynamic Performance of Geotextile-reinforced Embankment

Using geosynthetics in highway embankments can reduce theimpact of hazardous earthquakes by transmitting less excitationto improve the seismic performance. This study uses a 1-greduced scale (1/50) approach and subjects the model embankmentto an earthquake time history as well as several levelsof uniform cyclic loading. The main focus of comparison isbetween an unreinforced embankment and a one, reinforcedwith two levels of geosynthetics material. Results reveal thatgeotextile reinforced highway embankment models performmuch better under the applied motions. Larger amplitudes causemore severe deformations as a result of the increased dynamicloads. It is also revealed that the effectiveness of the geosyntheticsis dominated by the seismic frequency. Deamplificationis observed within the geotextile reinforced embankment but thedegree of deamplification is highly depended on the predominantfrequency of the dynamic load

Determining student difficulties in solving problems related to force and motion units via hint cards

WOS: 000361659800021In order to improve students' physics problem solving skills, the points which students have difficulty in during the problem solving process must be identified. in this study, It is aimed to determine the points in which students have difficulty in by using clinic interview method with the help of hint cards. 17 different problems related to 10th class "Force and Motion" unit have been designated and 9-11 different hint cards which have the same titles for each problem have been prepared. 17 problems have been solved by 21 students studying at 2 different schools in Trabzon. Firstly, all students have been asked to solve the given problems by thinking out loud, then, students who were able to solve the problem have been asked to tell the process in details and clearly; the students who have failed to solve the problems were asked to retry solving the same problem by using hint cards. Students have come up with the correct solution for some problems without using hint cards, while for some other problems; they have needed to use the hint cards. Whereas these students, despite using hint cards, could not come up with the correct solution to some problems. It was clearly seen that students have used the hint cards which include formulas and steps of solution mostly. It was determined that there ought to be a hint card about unit conversions and the "sample solution" hint should be expressed more clearly. It was retained that some students have had superficial problem solving approach and they have difficulty in making plan, an important step in problem solving; some students have little awareness about their own problem solving process and that proposing hints can help to solve the problem only to a certain extent. Teachers have been suggested to teach the simplest steps of the problems in a clear way, to give students enough time to solve the problems by themselves, to help students find their own wrong steps in the solution process. Accordingly, researchers have been suggested to determine the difficulties that students who are at different levels have while problem solving on different topics

Absolute co-supplement and absolute co-coclosed modules

A module M is called an absolute co-coclosed (absolute co-supplement) module if whenever M ≅ T/X the submodule X of T is a coclosed (supplement) submodule of T. Rings for which all modules are absolute co-coclosed (absolute co-supplement) are precisely determined. We also investigate the rings whose (finitely generated) absolute co-supplement modules are projective. We show that a commutative domain R is a Dedekind domain if and only if every submodule of an absolute co-supplement R-module is absolute co-supplement. We also prove that the class Coclosed of all short exact sequences 0→A→B→C→0 such that A is a coclosed submodule of B is a proper class and every extension of an absolute co-coclosed module by an absolute co-coclosed module is absolute co-coclosed.Scientific and Technical Research Council of Turke

Predicting energy absorption in a foam-filled thin-walled aluminum tube based on experimentally determined strengthening coefficient

The energy absorption in a foam-filled thin-walled circular Al tube was investigated based on the experimentally determined strengthening coefficient of filling using Al and polystyrene closed-cell foams with three different densities. Foam filling was found to change the deformation mode of tube from diamond (empty tube) into concertina, regardless the foam type and density used. Although foam filling resulted in higher energy absorption than the sum of the energy absorptions of the tube alone and foam alone, it was not effective in increasing the specific energy than simply thickening the tube wall. It was shown that for efficient foam filling an appropriate foam-tube combination must be selected by taking into account the magnitude of strengthening coefficient of foam filling and the foam filler plateau load.TÜBİTAK for the Grant # MISAG-22

Psoralea L. (fabaceae) cinsinin morfolojik, moleküler ve palinolojik revizyonu

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Bu çalışmada ülkemizde doğal olarak yayılış gösteren Psoralea L. cinsine ait türlerin morfolojik, moleküler ve palinolojik özellikleri araştırılmıştır. Ayrıca tür teşhis anahtarı ve betimleri yapılarak habitat özellikleri, IUCN kategorileri ve coğrafik yayılışları verilmiştir. Moleküler çalışmalar kapsamında Psoralea cinsine ait taksonların DNA?ları 2XCTAB metodunun modifiye edilmesiyle izole edilmiş ve 8 ISSR primeriyle PCR yapılmıştır. Elde edilen 246 polimorfik bant NTSYS-pc programında değerlendirilerek türler arasındaki filogenetik ilişkileri gösteren dendogram elde edilmiştir. Palinolojik çalışmalarda Türkiye Psoralea cinsine ait taksonların polenleri ışık ve taramalı elektron mikroskobunda (SEM) incelenmiştir.Cinsin Türkiye?deki taksonomik durumu net olarak ortaya konmuştur. Anahtar kelimeler: Türkiye, revizyon, Fabaceae, Psoralea, Bituminaria, Cullen.In this study, naturally occuring Psoralea L. species of Turkey were evaluated by means of morphological, molecular and palynological features. Habitat features, IUCN categories and geographical distributions of the species were also given with species identification keys and descriptions. Related to the molecular studies, DNAs were isolated according to 2XCTAB procedure, with minor modifications, and PCRs were conducted in the presence of 8 ISSR primers. Obtained 246 polymorphic bands by evaluating the programme NTSYS-pc dendogram showing the phylogenetic relationships among species were obtained. Pollens of the taxa belonging to the genus Psoralea in Turkey were examined with light and scanning electron microscopes. The taxonomic status of the genus in Turkey clearly revealed. Key Words: Turkey, revision, Fabaceae, Psoralea, Bituminaria, Cullen