The Role of Rubrene Concentration on Dielectric Parameters of Nematic Liquid Crystal

In this study, the dielectric parameters of E7 coded nematic liquid crystal (NLC) composites containing the different amounts of rubrene fluorescent dye were investigated. E7, E7+0.5 wt.% Rubrene, and E7+1.0 wt.% Rubrene samples were prepared. Frequency dependent dielectric constants (ɛ′ and ɛ′′), dielectric anisotropy (Δε′), and ac conductivity (σac) graphs of rubrene doped E7 NLC composites were obtained by dielectric spectroscopy method and compared with pure E7 NLC. By using these graphs, relaxation frequency (fR), relaxation time (τR), dielectric strength (δɛ′), and crossover frequency (fc) parameters of the E7 NLC and its rubrene doped composites were determined. An increase in fR from 3.045 MHz to 3.697 MHz for 0 V and from 627 kHz to 686 kHz for 40 V was observed with increasing rubrene concentration. On the other hand, a decrease in τR from 0.052 μs to 0.043 μs for 0 V and from 0.254 μs to 0.232 μs for 40 V was seen with increasing rubrene concentration. Furthermore, an increase in fc from 1.145 MHz to 1.298 MHz was obtained with increasing rubrene concentration. The results show that the dielectric parameters change with the concentration of rubrene and it is thought that this study will provide a basis for investigating the dielectric properties of rubrene doped NLC composites. Moreover, it is concluded that the produced composites are a suitable base material for electro-optical device applications such as smart displays, photonics and electrical circuit elements

Effects of CdTe Quantum Dot Dispersal on Current-Voltage Characteristics in Liquid Crystalline Mediums of E63, E7 and SCLP

The usage of nano-sized quantum dots (QDs) particularly in guest-host based hybrid mediums revealed enhancements in electro-optical properties of the mediums, therefore the focus of considerable amount of contemporary studies has been about dispersal of QDs for improvements in medium. This study investigates the effects of CdTe QD dispersal on current-voltage characteristics of some liquid crystalline materials such as E63, E7 and SCLP. Current is increased for all samples due to QD dispersal, however the best improvement is obtained for E7. Hence, current-voltage characteristics of E7 and QD dispersed E7 mediums were also investigated under UV light exposure. Current values of both mediums were found to increase with increasing UV light power due to generation of electron-hole pairs. Photocurrent’s dependence on light power revealed that QD dispersal does not affect recombination mechanism in the medium. On the other hand, UV light responsivity of QD dispersed E7 was obtained approximately twice of that of E7. Thus, it was concluded that CdTe QDs make considerable contribution to current-voltage and photoconductivity characteristics of E7 in dark and under UV light illumination

Fen ve Teknoloji Dersi İle Fen Bilimleri Dersi Öğretim Programlarının Öğrencilerin Araştırma Becerilerine Etkilerinin Karşılaştırılması

Bu çalışmanın amacı, 2005 yılı Fen ve Teknoloji dersi programı ile 2013 yılı Fen Bilimleri dersi programının öğrenci rollerinde ortak olarak ifade edilen araştıran ve sorgulayan bir birey yetiştirmek için gerekli olan araştırma becerilerinin öğrencilere kazandırılma durumlarının incelenmesidir. Tarama modelinde yürütülen bu çalışmada 2005 ve 2013 programları ile öğrenim görmüş öğrencilerin araştırma becerilerinin ortaya konulup karşılaştırılması amaçlanmıştır. Çalışmanın örneklemini Balıkesir ilinde öğrenim gören ve tabakalı amaçsal örnekleme yöntemi ile seçilmiş 1532 öğrenci oluşturmaktadır. Araştırma verileri Araştırma Becerileri Testi ve yarı yapılandırılmış görüşmeler ile toplanmıştır. Yapılan analizler sonucunda 2005 yılı Fen ve Teknoloji dersi öğretim programı ile öğrenim gören öğrencilerin araştırma becerilerinin 2013 yılı Fen Bilimleri dersi öğretim programı ile öğrenim gören öğrencilerden daha fazla geliştiği görülmüştür. Araştırma becerilerinin alt becerileri olarak belirlenen becerilerin de öğrencilere kazandırılma durumları incelenmiştir. Analiz sonuçları, öğrencilerin değişkenleri belirleme becerileri arasında anlamlı fark olmadığını ancak araştırılabilir soru belirleme, hipotez kurma, verileri kaydetme ve verileri yorumlama becerilerinde 2005 programı lehine anlamlı bir fark olduğunu göstermektedir. Çalışma sonunda yeni Fen Bilimleri programı da araştırma becerilerini kazanım düzeyinde ele alışı açısından değerlendirilmiş ve programın uygulayıcısı öğretmenlere öğrencilerin araştırmayı soru sorup cevap alma olarak görmemesi için sürecin takip edilmesi gibi önerilerde bulunulmuştur

Investigation of electro-optic and dielectric properties of CdSeS/ZnS quantum dot-doped 5CB nematic liquid crystals

YÖK Tez No: 523067Bu çalışmada, CdSeS/ZnS kuantum nokta katkılı 5CB (4-pentyl-4'-cyanobiphenyl) nematik sıvı kristal yapının elektro-optik ve dielektrik özellikleri incelenmiştir. CdSeS/ZnS kuantum nokta, 5CB nematik sıvı kristal içerisine ağırlıkça % 0,05, % 0,10 ve % 0,15 oranlarında katkılanmış ve sıvı kristal-kuantum nokta kompozit yapıları oluşturulmuştur. 5CB nematik sıvı kristal ve CdSeS/ZnS kuantum nokta katkılı 5CB nematik sıvı kristal kompozit yapıların elektrik ve dielektrik özellikleri 1 kHz-10 MHz frekans aralığında ve 0 V-20 V gerilim değerleri kullanılarak dielektrik spektroskopi tekniği ile incelenmiştir. Numunelerin optik özellikleri ise 300 nm-800 nm dalga boyu aralığında optiksel geçirgenlik spektroskopi yöntemi kullanılarak araştırılmıştır. Ölçüm sonuçlarından, 5CB nematik sıvı kristal ve CdSeS/ZnS kuantum nokta katkılı 5CB nematik sıvı kristal kompozit yapılara ait optik bant aralığı, kompleks dielektrik sabitinin reel ve sanal kısımları, dielektrik anizotropi, relaksasyon frekansı, geçiş frekansı, eşik voltajı, eğilme elastik sabiti ve relaksasyon zamanı parametreleri elde edilmiştir. Optik bant aralığı, eşik voltajı ve eğilme elastik sabiti parametrelerinin değerlerinin CdSeS/ZnS kuantum nokta katkılanması ile önemli ölçüde azaldığı gözlemlenmiştir. Ayrıca incelenen yapıların gerilime bağlı akım değerleri elde edilmiştir. Kuantum noktaların neden olduğu yük yoğunluğundaki artışa bağlı olarak, ortamdan geçen akım değerinin arttığı görülmüştür. Sonuçlar, CdSeS/ZnS kuantum noktaların 5CB nematik sıvı kristale katkılanması ile elde edilen kompozit yapılarda elektro-optik ve dielektrik özelliklerde önemli değişimlere neden olduğunu ve ortamın iletkenliğini arttırdığını göstermiştir.In this study, the electro-optic and dielectric properties of CdSeS/ZnS quantum dot doped 5CB (4-pentyl-4'-cyanobiphenyl) nematic liquid crystal structure were investigated. The CdSeS/ZnS quantum dot was doped into the 5CB nematic liquid crystal at a ratio of 0.05 %, 0.10 % and 0.15 % wt and liquid crystal-quantum dot composite structures were formed. Electric and dielectric properties of 5CB nematic liquid crystal and CdSeS/ZnS quantum dot doped 5CB nematic liquid crystal composite structures were investigated in the frequency range of 1 kHz-10 MHz and 0 V-20 V voltages with using dielectric spectroscopy method. The optical properties of the samples were investigated by optical transmission spectroscopy at a wavelength range of 300 nm-800 nm. The optical band gap, real and imaginary part of complex dielectric constant, dielectric anisotropy, the relaxation frequency, crossover frequency, threshold voltage, splay elastic constant and relaxation time parameters of 5CB nematic liquid crystal and CdSeS/ZnS quantum dot doped 5CB nematic liquid crystal composite structures were obtained using experimental data. The values of the optical band gap, threshold voltage and splay elastic constant parameters were found to decrease significantly with CdSeS/ZnS quantum dot doping. The voltage dependent current values of the investigated structures were also obtained. Depending on the increase in charge density caused by the quantum dots, the value of the current passing through the medium is increased. Results show that CdSeS/ZnS quantum dots cause significant changes in the electro-optic and dielectric properties of 5CB nematic liquid crystal composite structures and increase the conductivity of the mediums

Enhancement of electro-optical and dielectric properties of CdSeS/ZnS semiconductor quantum-dot-doped nematic liquid crystals in the presence of UV-illumination effect

WOS: 000468869000009In this study, we have investigated ultraviolet (UV) illumination effect on electro-optical and dielectric properties of varying concentration of CdSeS/ZnS semiconductor quantum-dot-doped 5CB nematic liquid crystal. Dielectric measurements were made from 10kHz to 10MHz frequency ranges in dark and under UV-illumination conditions. Electro-optical measurements were also performed with a voltage-dependence light transmission system at 10kHz frequency in dark and under UV-illumination conditions. Significant physical parameters such as relaxation frequency (f(R)), real and imaginary components of complex dielectric permittivity (epsilon and epsilon), and threshold voltage (V-th) values were obtained from experimental results. Results show that UV-illumination effects cause considerable improvements on electro-optical and dielectric characteristic of investigated samples.Duzce University Scientific Research ProjectDuzce University [2018.05.02.811]This work supported financially by Duzce University Scientific Research Project (Project No: 2018.05.02.811)

TEACHING FOR HOT CONCEPTUAL CHANGE: TOWARDS A NEW MODEL, BEYOND THE COLD AND WARM ONES

At the beginning of the 1980’s, one of the most striking explanation of conceptual change was made by Posner, Strike, Hewson & Gertzog (1982) with a Conceptual Change Theory based on a Scientific Revolution Theory of Kuhn (1970). In Conceptual Change Theory, learning was explained with the Piaget (1970)’s concepts such as assimilation and accommodation. Especially at the beginning of 1990, the Conceptual Change Theory was called as a cold conceptual change, for solely taking the cognitive factors of individuals, and for not taking the affective factors like motivation into consideration (Pintrich, Max & Boyle, 1993). In their studies Tyson, Venville, Harrison & Treagust (1997) (1997) and Alsop & Watts suggested a multidimensional structure of conceptual change including affective characteristics. Dole & Sinatra (1998) have emphasized information processing in conceptual change and have also described the impact of motivation on conceptual change in their Cognitive Reconstruction of Knowledge Model. The Authors explain how the affective and cognitive characteristics interact each other, and they come up with the warming trend in the conceptual change. Gregoire (2003) has emphasized the automatical evaluation of message and emotions such as fear and anxiety. In order to show how these constructs effect conceptual change, the author has proposed Cognitive Affective Model of Conceptual Change called Hot Conceptual Change. According to the Zhou (2010), although hot factors, such as motivation, are added up to the conceptual change models cumulatively in time, they have little evidence at the point of science teaching. Author proposed a model called “Argumentation Approach in Teaching Science” in order to raise temperature in science teaching by using argumentation approach. In this study, we tried to raise temperature more than Zhou (2010) did and started hot trend in science teaching. In this paper, conceptual change literature has been summarized and our teaching model based on a hot conceptual change and supported by motivational and metacognitive strategies has been introduced. Furthermore, application of our hot model to the Photoelectric Effect Teaching was presented

A content analysis related to studies carried out on project-based learning method in science education

Bu çalışma Türkiye’de fen eğitimi alanında proje tabanlı öğrenme yaklaşımını konu edinen makalelerin ve tezlerin incelenmesine ait bir içerik analizi çalışmasıdır. Bu amaçla 2002-2019 yılları arasında yapılan yayınlar incelenmiş ve bu çalışmaların yayın yılı, yayın türü, örneklem türü, araştırma yöntemi, araştırma konusu, araştırma alanı, örneklem belirleme yöntemi, veri toplama araçları, veri analiz yöntemi, araştırma sonuçları ve bulgularına göre dağılımları grafik, yüzde tablosu ve frekans olarak açıklanmıştır. Çalışmada proje tabanlı öğrenme ile ilgili 31 makale, 42 yüksek lisans tezi ve 9 doktora tezi olmak üzere 82 çalışmaya ulaşılmıştır. Çalışma sonucunda proje tabanlı öğrenme yaklaşımı ile ilgili fen eğitimi alanında yapılan çalışmaların 2008–2011 yılları arasında artış gösterdiği, yayın türüne göre yüksek lisans tezlerinin çoğunlukta olduğu, örneklem türüne göre orta öğretim düzeyinde ve araştırma alanı incelendiğinde ise fen ve teknoloji alanında daha çok çalışma yapıldığı ve nicel araştırmaların sayısının daha çok olduğu görülmektedir. Ayrıca araştırma konusu olarak proje tabanlı öğrenme yaklaşımının başarı değişkeni açısından karşılaştırıldığı ve etkisinin belirlenmeye çalışıldığı; veri analiz yöntemi olarak ise t-testinin ön plana çıktığı ve araştırmaların sonuç ve bulgularına göre proje tabanlı öğrenme yaklaşımının fen eğitiminde akademik başarıyı ve tutumu arttırdığı sonucuna ulaşılmıştır.This study is a content analysis based on the examination of articles and theses which are the subject of project-based learning method in the field of science education in Turkey. For this purpose, literature review was conducted to examine the publications between the years 2002 and 2019. Studies concerning project-based learning were grouped by preparing frequency and percentage tables and graphs according to year of publication, publication type, sample type, research method, research topic, research field, sample determination method, data collection instruments, data analysis method, along with research findings and results accordingly. In this study, it has been reached a total of 82 studies (42 master’s theses, 9 doctoral theses and 31 articles) carried out on project-based learning. As a result of the study, the studies conducted in the field of science education related to the project based learning approach increased between the years 2008-2011, according to the type of publication, master theses are the majority, according to the sample type, it is seen that there are more studies in the field of science and technology and the number of quantitative researches is higher when the secondary education level and research field are examined. Additionally, project-based learning method was compared in terms of the variable ‘success’ and attempted to determine its effect under research topics; t-test was foregrounded as a data analysis method and according to research findings and results, it has been achieved that project-based learning method in science education increases the academic success and attitude accordingly

Investigation of Optical Band Gap of CdSeS/ZnS Quantum Dot Doped 5CB Nematic Liquid Crystals

Bu çalışmada, CdSeS/ZnS alaşım kuantum nokta katkılı 5CB (4-pentyl-4?-cyanobiphenyl) nematik sıvı kristal yapının optik bant aralığı değerleri incelenmiştir. CdSeS/ZnS alaşım kuantum nokta, 5CB nematik sıvı kristal yapı içerisine ağırlıkça % 0,05, % 0,1 ve % 0,15 oranlarında katkılanarak optik bant aralığı değerleri elde edilmiştir. Deneysel sonuçlara göre kuantum nokta katkılanmasıyla optik bant aralığı değerlerinin azaldığı gözlemlenmiştir. Elde edilen sonuçlar, CdSeS/ZnS alaşım kuantum nokta yapının sıvı kristal tabanlı cihaz uygulamalarında elektrooptik özellikleri değiştirebilen alternatif bir malzeme olarak kullanılabileceğini göstermektedirIn this study, optical band gap values of 5CB (4-pentyl-4 'cyanobiphenyl) nematic liquid crystal structure doped with CdSeS/ZnS alloyed quantum dots are investigated. The CdSeS/ZnS alloyed quantum dot was doped into the 5CB nematic liquid crystal structure at 0.05, 0.1 and 0.15 % wt/wt and optical band gap values were obtained. According to experimental results, optical band gap values decrease with quantum dot doping. The results show that the CdSeS/ZnS alloyed quantum dots can be alternative materials used in liquid crystal based device applications whose electro-optical properties are able to be easily modifie

Effect of intermolecular charge transfer between Ni(II)Pc and CdSeS/ZnS QD on dielectric relaxation mechanism of 5CB nematic liquid crystals in the presence of UV illumination

WOS: 000512889300085This paper is a report on electro-optical and dielectric parameters of Ni(II)Pc (nickel(II) phthalocyanine) and CdSeS/ZnS (cadmium selenide sulfide/zinc sulfide) quantum dot (QD) doped 5CB (4-pentyl-4 '-cyanobiphenyl) nematic liquid crystal (LC) in the dark and under UV illumination condition. Electro-optical and dielectric measurements of the samples were carried out using electro-optical switching and dielectric spectroscopy methods, respectively. Dielectric anisotropy, relaxation frequency, dielectric strength, and threshold voltage values were determined using the experimental data. Investigation of dielectric properties demonstrates that relaxation frequency is decreased because of the dispersal of Ni(II)Pc and CdSeS/ZnS QD under UV exposure. The electro-optical investigation also shows that UV illumination and dispersal of Ni(II)Pc and CdSeS/ZnS QD cause a decrease in threshold voltages. Overall, results indicate that Ni(II)Pc, CdSeS/ZnS QD and UV light enhanced the electro-optical and dielectric properties of 5CB nematic LC

Electro-optical and dielectric performance analysis: the influence of azo dye on polymer/LC composite structures

WOS: 000453519000001In the present work, electro-optical and dielectric properties of polymer/LC doped with azo dye methyl red (MR) were investigated. Norland optical adhesive (NOA65) and nematic liquid-crystal (E63-coded nematic liquid crystal) materials were used to compose of polymer/LC composite structure. A doping agent ratio of MR was chosen 1% wt/wt in polymer/LC composite structure. Dielectric measurements of the obtained samples were held between 10Hz and 10MHz at room temperature using dielectric/impedance analyzer. Physical parameters such as dielectric permittivity, dielectric anisotropy, electric modulus, loss tangent, relaxation frequency, relaxation time, threshold voltage, and splay elastic constant were obtained from experimental data. Optical bandgap values of polymer/LC and polymer/LC/MR composite structures were estimated using UV spectroscopy technique. Polymer/LC composite structures' electro-optical properties were affected the MR dispersal which was reduced the anchoring force between polymer and LC molecules; therefore, threshold voltage and splay elastic constant decreased. In addition, dispersal of MR caused a decrease in optical bandgap values of polymer/LC composite structures. Due to the increase in charge density caused by MR, the value of the current passing through the polymer/LC composite structures increased as well as its dependence on voltage. Results show that MR dispersal enhanced electro-optical and dielectric properties of polymer/LC composite structures and makes it suitable to design new based on optoelectronic device applications.Duzce University Scientific Research ProjectDuzce University [2018.05.02.811]This work supported financially by Duzce University Scientific Research Project (Project No: 2018.05.02.811)