Torsional characteristics of carbon nanotubes: Micropolar elasticity models and molecular dynamics simulation

Efficient application of carbon nanotubes (CNTs) in nano-devices and nano-materials requires comprehensive understanding of their mechanical properties. As observations suggest size dependent behaviour, non-classical theories preserving the memory of body’s internal structure via additional material parameters offer great potential when a continuum modelling is to be preferred. In the present study, micropolar theory of elasticity is adopted due to its peculiar character allowing for incorporation of scale effects through additional kinematic descriptors and work-conjugated stress measures. An optimisation approach is presented to provide unified material parameters for two specific class of single-walled carbon nanotubes (e.g., armchair and zigzag) by minimizing the difference between the apparent shear modulus obtained from molecular dynamics (MD) simulation and micropolar beam model considering both solid and tubular cross-sections. The results clearly reveal that micropolar theory is more suitable compared to internally constraint couple stress theory, due to the essentiality of having skew-symmetric stress and strain measures, as well as to the classical local theory (Cauchy of Grade 1), which cannot accounts for scale effects. To the best of authors’ knowledge, this is the first time that unified material parameters of CNTs are derived through a combined MD-micropolar continuum theory

Prediction of Breast Cancer Risk in Women over 35 Years Old Living in Villages of Zanjan: A Study Based on Gail Model

Background: Breast cancer is one of the most important malignancies in both developed and developing countries. Objectives: To reduce the burden of this disease, the prediction of individuals at risk and implementation of efficient preventive interventions can be effective. The present study was aimed at investigating five-year and lifetime risks of the breast cancer in a rural community in Zanjan province, Iran. Methods: A total of 435 subjects aged 35 years old were randomly selected using systematic randomization in a rural community in Zanjan. The participation rate was 92.4% (402 women). Data collection instrument was a questionnaire in which all associated variables of Gail model and demographic information were included. The data were analyzed using SPSS software version 18, and mean cancer risks were reported. Results: Family history of breast cancer and history of breast biopsy were found to be positive in 3.5% and 0.3% of participants, respectively. Out of all participants, 84.3% were under 60 years old and 13.2% were illiterate. Five-year and lifetime mean risks were fund to be 0.74% and 7.6%, respectively. About 2% of the participants had a higher cancer risk>1.66%. Conclusion: The findings demonstrated that based on the Gail model, the lifetime risk of the participants will be one out of 13 women. Given the lower estimations of Gail model in the prediction of breast cancer, we suggest general population interventions and high-risk strategies be implemented to decrease problems associated with the breast cancer in the future

Vibration analysis of viscoelastic single-walled carbon nanotubes resting on a viscoelastic foundation

Vibration responses were investigated for a viscoelastic Single-walled carbon nanotube (visco-SWCNT) resting on a viscoelastic foundation. Based on the nonlocal Euler-Bernoulli beam model, velocity-dependent external damping and Kelvin viscoelastic foundation model, the governing equations were derived. The Transfer function method (TFM) was then used to compute the natural frequencies for general boundary conditions and foundations. In particular, the exact analytical expressions of both complex natural frequencies and critical viscoelastic parameters were obtained for the Kelvin-Voigt visco-SWCNTs with full foundations and certain boundary conditions, and several physically intuitive special cases were discussed. Substantial nonlocal effects, the influence of geometric and physical parameters of the SWCNT and the viscoelastic foundation were observed for the natural frequencies of the supported SWCNTs. The study demonstrates the efficiency and robustness of the developed model for the vibration of the visco-SWCNT-viscoelastic foundation coupling system

Resimde İnsan ve Doğa İlişkisi

The history of humanity has been side by side with nature since the first existence of man. The human being, which shows its existence through the formation of the world together with the other creatures, has achieved a harmony against nature in the same way that the other creatures have done. Afterwards, the human being has partly obtained its superiority over nature by using his thoughts and ideas which make it different from other beings. Mankind’s start for recognizing the nature has caused to find new inventions within this long period and to make discoveries that mean revolution for itself. In other words, man has always been intertwined with nature, and strengthened their existence by recognizing nature. Human relations with nature has emerged from the first ages even in the field of art. Related with the time process, the different and developing needs of man have been shown in the field of art. Sometimes, art works have been symbols carrieng the magical meanings and sometimes, have turn into ornamental and written language. Sometimes, art has been beside the power and sometimes has reflected the social expression. In short, I would like to say that the relationship between art and nature will always continue to exist. Because man will always live with nature, and as long as this interaction exists, the human's connection to nature will manifest itself in the sense of science and art. The subject of this thesis is to visualize the relation of man to nature with my own interpretation. Human by its nature has been sometimes sad and sometimes warm and hopeful, just like nature. To reflect the existence of this harmony and similarity and to illustrate it with visual forms has been my goal in this thesis and the motivation of this research has intrigued me for this study.İnsanlık tarihi insanın ilk varoluşundan itibaren doğa ile yan yana olmuştur. Dünya oluşumunun içerisinde diğer canlılarla beraber varlığını gösteren insan tıpkı başka canlılar gibi doğaya karşı bir uyum sağlamıştır. Daha sonra ise insan diğer varlıklardan farklı olarak düşüncelerini ortaya koyarak doğaya karşı üstünlüğünü kısmen de olsa sağlamıştır. İnsanın doğayı tanımaya başlaması varoluşu süresince yeni buluşlar bulmasına ve devrim niteliğinde keşifler yapmasına sebep olmuştur. Yani insan her zaman doğayla iç içe olmuş ve doğayı tanıyarak varlığını daha da güçlendirmiştir. İnsanın doğayla ilişkisi sanat alanında bile ilk çağlardan itibaren kendisini göstermiştir. Zamanla insanın farklı ve gelişen ihtiyaçları sanat alanında da kendini göstermiştir. Sanat çalışmaları bazen büyüsel anlamlar taşıyan semboller olmuş bazen de süs ve yazı diline dönüşmüştür. Sanat kimi zaman güçlerin yanında yer almış kimi zaman da toplumsal ifadeyi yansıtmıştır. Sanat her zaman doğayla olan ilişki varlığını sürdürecektir. Çünkü insan doğayla her zaman yaşayacak ve bu etkileşim var olduğu sürece insanın doğayala irtibatı bilim ve sanat anlamında kendini gösterecektir. Bu tezin konusu, insanın doğayla ilişkisini kişisel yorumumlarla görselleştirmektir. İnsan doğası gereği tıpkı doğa gibi bazen hüzünlü bazen de sıcak ve umutlu olmuştur. Bu uyum ve benzerliği yansıtmak ve bunu görsel formlarla resimlendirmek bu tezin ana hedefi olmuştur

Molecular dynamics simulations of structural instability of fullerene family under tension force

Fullerene molecules are cage-like nanoscopic structures with pentagonal and hexagonal faces. In practical applications such as fullerene-reinforced nanocomposites (FRNCs), these structures may be subjected to tension force. In this research, we employ molecular dynamics (MD) simulation to compute the behaviour and deformation of different fullerene molecules, ranging from C60 to C2000, under tension force. To model the interactions between carbon atoms in the MD simulations, the adaptive intermolecular reactive bond order (AIREBO) force field is used. The displacement–force and the displacement–strain energy curves are obtained. It is observed that a new type of structural instability occurs in the fullerene molecules when the applied tension force increases. This abnormal structural instability in the fullerenes is investigated for the first time in the literature. The critical tensile forces and the corresponding mode shapes are determined for different fullerenes. The results indicate that the critical forces and deformations strongly depend upon the number of carbon atoms

Elastic properties of polymer composites reinforced with C60 fullerene and carbon onion: Molecular dynamics simulation

In this paper, the elastic properties of polymer nanocomposites reinforced with C60 fullerene and C60@C240 carbon onion are estimated by using a molecular dynamic (MD) simulation. The nanocomposites are constructed by embedding the buckminsterfullerene and the carbon onion into an amorphous polymer matrix with different weight fractions. The poly methyl methacrylate (PMMA) is chosen as the polymer matrix. The results demonstrate that Young's modulus of the composite increases with increasing the weight fractions of the nanoscopic additives, which is consistent with experimental observations. The nanocomposite containing 4 wt% of C60 exhibits Young's modulus of 3.774 GPa that is 24% higher than pure PMMA. In addition, the validity of the present simulation is verified by the comparison with the experimental results