Browsing by Subject "Physical properties"

Now showing 1 - 8 of 8

Open Access
Animation of deformable models
(Pergamon Press, 1994) Güdükbay, Uğur; Özgüç, B.
Although kinematic modelling methods are adequate for describing the shapes of static objects, they are insufficient when it comes to producing realistic animation. Physically based modelling remedies this problem by including forces, masses, strain energies and other physical quantities. The paper describes a system for the animation of deformable models. The system uses physically based modelling methods and approaches from elasticity theory for animating the models. Two different formulations, namely the primal formulation and the hybrid formulation, are implemented so that the user can select the one most suitable for an animation depending on the rigidity of the models. Collision of the models with impenetrable obstacles and constraining of the model points to fixed positions in space are implemented for use in the animations. © 1994.
Open Access
Dielectric inspired scaling of polarization conversion subwavelength resonances in open ultrathin chiral structures
(A I P Publishing LLC, 2015) Serebryannikov, A. E.; Mutlu, M.; Özbay, Ekmel
It is shown that the scaling of subwavelength resonances in open ultrathin chiral structures can be obtained by varying only the permittivity of dielectric spacers, while multiband one-way polarization conversion and related asymmetric transmission remain possible. These features are quite general and obtainable in a wide range of parameter variation. Surprisingly, the difference in the power of ε for the classical ε-1/2 scaling rule and the empirical rules obtained in the present letter does not exceed 22%, giving an important entry point for future theoretical studies and design strategies. Both spectral scaling and conservation of the polarization characteristics can be achieved by using either tunneling or real-index impedance matching. The scaled structures with strong polarization and directional selectivity may have thickness of λ/100 and smaller. © 2015 AIP Publishing LLC.
Open Access
Interaction of adatoms and molecules with single-layer arsenene phases
(American Chemical Society, 2016-06) Ersan, F.; Aktürk, E.; Çıracı, Salim
Recent studies have shown that arsenic can form single-layer phases in buckled honeycomb as well as symmetric washboard structures, named as arsenene. These structures are stable even in freestanding form and are nonmagnetic semiconductors in the energy range which is suitable for various electronic applications. In this study we investigated the adsorption of selected adatoms (H, Li, B, C, N, O, Al, Si, P, Cl, Ti, Ga, Ge, As, Se, and Sb) and physisorption of molecules (H2, O2, and H2O) to these two arsene phases. Since the interaction of these adspecies with arsenene are studied using large supercells, the coupling between adspecies is minimized, and hence our results can be interpreted to mimic the effects of isolated adatom or physisorbed molecule. It is found that the adatoms form strong chemisorption bonds and hence modify the atomic structure and physical properties locally. Some of the adatoms give rise to significant local reconstruction of the atomic structure. Electronic states of some adatoms become spin polarized and attain net magnetic moments; they may even display half-metallic character at high coverage. A majority of adsorbed atoms give rise to localized states in the fundamental band gap. We showed that the interactions between H2, O2, and H2O molecules and single-layer arsenene are rather weak and do not cause any significant changes in the physical properties of these molecules, as well as those of arsenene phases. However, some of these molecules can be dissociated at the edges of the flakes of arsenene structures; their constituents are adsorbed to the edge atoms and cause local reconstructions.
Open Access
Interlocking shish-kebab morphology in polybutene-1
(John Wiley & Sons, Inc., 2002) Kalay, G.; Kalay, C. R.
The aim of this research was to explore the effect of shear-controlled orientation injection molding (SCORIM) on polybutene-1 (PB-1). This article describes the methods and processing conditions used for injection molding and discusses the properties of the moldings. Both conventional and SCORIM have been used for the production of moldings. SCORIM is based on the application of specific macroscopic shears to a solidifying melt that facilitates enhanced molecular alignment. The effect of the process was investigated by performing mechanical tests, X-ray studies, differential scanning calorimetric studies, polarized light microscopy, and atomic force microscopy (AFM). Moldings exhibited an improved mechanical performance as compared with conventional moldings. Young's modulus was increased over twofold, and the impact energy was enhanced by 60%. The improvement in mechanical performance was combined with an increase in crystallinity and enhanced molecular orientation. The application of SCORIM also favored the formation of the stable Form I' in PB-1. The formation of interlocking shish-kebab morphology following the application of SCORIM was observed in the AFM studies. Relationships between the mechanical properties of PB-1 and the micromorphologies formed during processing are demonstrated.
Open Access
Investigation and control of the static electrification in polypropylene
(2016-08) Yavuz, Zelal
The electrostatic charging of polymers due to friction is such a common phenomenon in daily usage of polymers that can be a problematic issue for various applications, such as in electronic devices, textile, space industry and so on. Hence, understanding and controlling of the mechanism behind the static electrification, which is basically because of the charge accumulation on the material, is an important subject in terms of the applications. In the way to understand static electrification of bulk materials, examining the physical and morphological properties is crucial. On the other hand, when the physical properties are considered, the structure of polymer plays a significant role, yet there is a lack of knowledge in the literature about the relation between these structural properties and triboelectricity. As a reason of this, it can be pointed out that in the proposed mechanisms about the frictional electrification the structure-property relation could not get sufficient attention so far. In this thesis, the crystalline structure of polymer, which plays a crucial role in the determination of physical properties of polymeric materials, was studied and by using different treatment techniques, such as microwave radiation and mechanical stress, and the relation between the degree of crystallinity and triboelectric charging was investigated. Due to its economical cost and heat-sensitive degree of crystallinity that can be changed in a significant way polypropylene (PP) which is a semi-crystalline polymer was used in this study. Hence, by utilizing different spectroscopic and microscopic techniques the relation between physical properties and triboelectrification of polypropylene was investigated in detail. In order to understand the physical and chemical changes taking place in untreated and treated polypropylene X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Differential Scanning Calorimetry (DSC) are the techniques that were employed. In this study, by considering the mechanism behind static electrification the potential link between electrification and degree of crystallinity was designated. Furthermore, the generation of charge on the surface of mechanically treated polypropylene film was observed for the first time by this current work. The results lead to the fact that it is possible to convert mechanical energy into electrical energy without any contact between the objects by introducing physical forces onto the insulating materials and the reasons behind non-contact electrification was investigated. Therefore, in the light of the results obtained from this study, more efficient triboelectric generators can be designed to harvest electrical energy from mechanical energy.
Open Access
Lattice dynamics and elastic properties of lanthanum monopnictides
(2008) Gökoǧlu G.; Erkişi, A.
In this study, first principles calculation results of the second order elastic constants and lattice dynamics of two lanthanum monopnictides, LaN and LaBi, which crystallize in rock-salt structure (B1 phase), are presented. Calculations were based on plane wave basis sets and pseudopotential methods in the framework of Density Functional Theory (DFT) with generalized gradient approximation. Elastic constants are calculated by tetragonal and orthorhombic distortions on cubic structure. Phonon dispersion spectra was constructed in the linear response approach of the Density Functional Perturbation Theory (DFPT). The complete phonon softening with negative frequencies and large elastic anisotropy were observed for LaN single crystal as a sign of the structural instability. The phonon dispersion curve for LaBi is typical for lanthanum monopnictides and does not show any anomalous physical property. The calculated structural quantities for both LaN and LaBi systems agree well with the available experimental and theoretical data. © 2008 Elsevier Ltd. All rights reserved.
Open Access
A measurable force driven by an excitonic condensate
(American Institute of Physics Inc., 2014) Hakioǧlu, T.; Özgün, E.; Günay, M.
Free energy signatures related to the measurement of an emergent force (≈10-9N) due to the exciton condensate (EC) in Double Quantum Wells are predicted and experiments are proposed to measure the effects. The EC-force is attractive and reminiscent of the Casimir force between two perfect metallic plates, but also distinctively different from it by its driving mechanism and dependence on the parameters of the condensate. The proposed experiments are based on a recent experimental work on a driven micromechanical oscillator. Conclusive observations of EC in recent experiments also provide a strong promise for the observation of the EC-force. © 2014 AIP Publishing LLC.
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Prediction of new generation two-dimensional ternary structures and investigation of their fundamental properties
(2023-05) Varjovi, Mirali Jahangirzadeh
Consecutive to the isolation of graphene and uncovering its extraordinary properties, the dynasty of two-dimensional (2D) materials has expanded rapidly. A realization of every new member suggests novel features, holding the promise to be used in current and prospective nanodevices. In parallel with the attempts on exploring new 2D systems, the formation of ternary configurations has been suggested as an alternative approach to tailor the inherent properties of the already existing 2D structures. In accordance with recent advancements in ternary 2D systems, in this dissertation, we design and investigate the 2D systems which possess three types of elements in their crystal structure. In this regard, we design Janus Al2XX′ (X/X′: O, S, Se, Te) crystals, 1H, 1T, and 1T′ phases of Janus WXO (X = S, Se, and Te) monolayers and Janus BiXY (X= S, Se, Te, and Y = F, Cl, Br, I ) nanosheets and investigate their structural, vibrational, elastic, piezoelectric, and electronic properties by first-principle methods. In addition, inspired by the synthesis of penta-Si nanoribbons, advancements in 2D pentagonal systems, and recent developments on ternary structures, we propose and investigate a new ternary pentagon-based 2D monolayer, namely penta-BNSi. We study the mechanical, electronic, piezoelectric, photocatalytic, and optical properties of penta-BNSi crystal and reveal its suitability to be used in optoelectronics and photocatalytic applications. Then, we focused our attention on new family of MA2Z4 monolayers. Based on this motivation, we perform a comprehensive study on physical properties of MSi2Z4 (M: Pd and Pt, Z: N and P) monolayers and suggested novel single layer of InSiN2 (In2Si2N4). For this purpose, in both studies, the ground state configurations of the designed materials are determined, and then the dynamical and thermal stability of these nanosheets are investigated using phonon spectrum analysis and ab initio molecular dynamic (AIMD) simulations, respectively. Next, each structure’s Raman and infrared (IR) spectrum are analyzed, and the corresponding atomic displacements of the optical phonon modes are presented. Then, the mechanical properties are studied in terms of in-plane stiffness and Poisson’s ratio. The electronic band structures are computed in the electronic properties section, and the corresponding energy band gaps are reported. For MSi2Z4 (M: Pd and Pt, Z: N and P) monolayers, the optical response is examined via calculation of the complex dielectric function by taking many-body interactions into account. In the final study, the effect of an external biaxial strain on the electronic and vibrational properties of the InSiN2 nanosheet is investigated, and the variation of the obtained properties under strain is illustrated. As a result of a thorough theoretical study focusing on ternary 2D materials, it can be said that the examined crystals are stable systems with potential applications in a wide range of nanoelectronics and nanomechanical devices.