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Analysis of birefringence property of three different nematic liquid crystals dispersed with TiO₂ nanoparticles

Pathak G., Katiyar R., Agrahari K., Srivastava A., Dabrowski R., Garbat K., Manohar R.

Opto-Electronics Review

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2018

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Vol. 26, No. 1

11--18

EN

In the present work TiO₂ nanoparticles (NPs) have been dispersed into three different nematic liquid crystals (2020, 1823A and 1550C) in different concentration. The value of the birefringence (Δn) has been calculated by the transmitted intensity method at a 632.8 nm wavelength. NLC 2020 used in the present study is a high birefringent material (Δn = 0.44), NLC 1550C is a low birefringent material (Δn = 0.067) and NLC 1823A is a mid birefringent material (Δn = 0.14). An increased value of birefringence has been found after dispersion of TiO₂ NPs in all three NLCs but this increment depends upon the concentration of the dopant material, temperature range and chemical character of the mixtures. It is suggested that this LC materials can be applicable in making of phase shifters, compensators and many more photonic devices.

2

Applying Machine Learning to Software Fault Prediction

Wójcicki B., Dabrowski R.

e-Informatica Software Engineering Journal

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2018

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Vol. 12, nr 1

199--216

EN

Introduction: Software engineering continuously suffers from inadequate software testing. The automated prediction of possibly faulty fragments of source code allows developers to focus development efforts on fault-prone fragments first. Fault prediction has been a topic of many studies concentrating on C/C++ and Java programs, with little focus on such programming languages as Python. Objectives: In this study the authors want to verify whether the type of approach used in former fault prediction studies can be applied to Python. More precisely, the primary objective is conducting preliminary research using simple methods that would support (or contradict) the expectation that predicting faults in Python programs is also feasible. The secondary objective is establishing grounds for more thorough future research and publications, provided promising results are obtained during the preliminary research. Methods: It has been demonstrated that using machine learning techniques, it is possible to predict faults for C/C++ and Java projects with recall 0.71 and false positive rate 0.25. A similar approach was applied in order to find out if promising results can be obtained for Python projects. The working hypothesis is that choosing Python as a programming language does not significantly alter those results. A preliminary study is conducted and a basic machine learning technique is applied to a few sample Python projects. If these efforts succeed, it will indicate that the selected approach is worth pursuing as it is possible to obtain for Python results similar to the ones obtained for C/C++ and Java. However, if these efforts fail, it will indicate that the selected approach was not appropriate for the selected group of Python projects. Results: The research demonstrates experimental evidence that fault-prediction methods similar to those developed for C/C++ and Java programs can be successfully applied to Python programs, achieving recall up to 0.64 with false positive rate 0.23 (mean recall 0.53 with false positive rate 0.24). This indicates that more thorough research in this area is worth conducting. Conclusion: Having obtained promising results using this simple approach, the authors conclude that the research on predicting faults in Python programs using machine learning techniques is worth conducting, natural ways to enhance the future research being: using more sophisticated machine learning techniques, using additional Python-specific features and extended data sets.

3

Pieniądze z powietrza, czyli jak zarobić na odnawialnych źródłach energii

Dabrowski R.

Dozór Techniczny

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2015

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z. 3

8--11

PL

W najbliższych latach w Polsce będzie rósł udział odnawialnych zródeł energii (OZE) w całkowitym bilansie energetycznym kraju. Przynajmniej tak wynika z polityki Unii Europejskiej i polskich zobowiązań. W dokumentach rządowych wiodącą pozycje wśród OZE zarezerwowano dla energii wiatrowej. - Postawienie wiatraka to droga przez mękę - mówi jednak przedsiębiorca z Radomska, który cztery lata temu wybudował elektrownie o mocy 0,5 MW na wieży o wysokości 65 metrów. I wątpi w powodzenie tego przedsięwzięcia.

4

Study of optical parameters of two fluorinated isothiocyanato nematic liquid crystals exhibiting high birefringence

Devi T. K., Choudhury B., Bhattacharjee A., Dabrowski R.

Opto-Electronics Review

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2014

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Vol. 22, No. 1

24-30

EN

Optical studies have been carried out on two fluorinated isothiocyanato nematic liquid crystal (LC) compounds 4'-butylcyclohexyl-3, 5-difluoro-4-isothiocyanatobiphenyl and 4'-pentylcyclohexyl-3, 5-difluoro-4- isothiocynatobiphenyl. Transition temperatures of the two samples were confirmed using a polarizing microscope. The two LC compounds were found to exhibit fairly high clearing temperatures. Measurements of refractive indices of the two compounds were done by using thin prism method with He-Ne laser beam of wavelength 630 nm. Birefringence of the two LC compounds was calculated from the measured refractive indices. Both the compounds are found to display fairly high values of birefringence. Validation of a modified four-parameter model, based on Vuks equation describing the temperature dependence of refractive indices of the two liquid crystals, is also presented in this paper. The model is validated by fitting the experimentally measured values of refractive indices, birefringence and average refractive indices of the two nematic LCs with the theoretical values. In this paper, the calculation of order parameters of the LCs is presented by using two methods: direct extrapolation method based solely on the birefringence data and by using modified Vuks method based on Haller’s extrapolation. As observed from the obtained results, this procedure of calculating order parameter gives very reasonable results.

5

On Visual Assessment of Software Quality

Bartoszuk C, Timoszuk G., Dabrowski R., Stencel K.

e-Informatica Software Engineering Journal

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2014

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Vol. 8, nr 1

7--26

EN

Development and maintenance of understandable and modifiable software is very challenging. Good system design and implementation requires strict discipline. The architecture of a project can sometimes be exceptionally difficult to grasp by developers. A project’s documentation gets outdated in a matter of days. These problems can be addressed using software analysis and visualization tools. Incorporating such tools into the process of continuous integration provides a constant up-to-date view of the project as a whole and helps keeping track of what is going on in the project. In this article we describe an innovative method of software analysis and visualization using graph-based approach. The benefits of this approach are shown through experimental evaluation in visual assessment of software quality using a proof-of-concept implementation — the Magnify tool.