GCRIS Repository Collection: Collection of Physics / Fizik Bölümü koleksiyonu
https://hdl.handle.net/11147/6
Collection of Physics / Fizik Bölümü koleksiyonu
20240617T04:48:51Z

Modeling cosmological perturbations of thermal inflation
https://hdl.handle.net/11147/14249
Title: Modeling cosmological perturbations of thermal inflation
Authors: Bae, JeongMyeong; Hong, Sungwook E.; Zoe, Heeseung
Abstract: We consider a simple system consisting of matter, radiation and vacuum components to model the impact of thermal inflation on the evolution of primordial perturbations. The vacuum energy magnifies the primordial modes entering the horizon before its domination, making them potentially observable, and the resulting transfer function reflects the phase changes and energy contents. To determine the transfer function, we follow the curvature perturbation from well outside the horizon during radiation domination to well outside the horizon during vacuum domination and evaluate it on a constant radiation density hypersurface, as is appropriate for the case of thermal inflation. The shape of the transfer function is determined by the ratio of vacuum energy to radiation at matterradiation equality, which we denote by upsilon , and has two characteristic scales, ka and kb , corresponding to the horizon sizes at matter radiation equality and the beginning of the inflation, respectively. If upsilon MUCH LESSTHAN1 , the Universe experiences radiation, matter and vacuum domination eras and the transfer function is flat for kMUCH LESSTHANkb , oscillates with amplitude 1/5 for kbMUCH LESSTHANkMUCH LESSTHANka and oscillates with amplitude 1 for k >> ka . For upsilon >> 1 , the matter domination era disappears, and the transfer function reduces to being flat for kMUCH LESSTHANkb and oscillating with amplitude 1 for k >> kb .
20240101T00:00:00Z

Chlorinated phosphorene for energy application
https://hdl.handle.net/11147/14128
Title: Chlorinated phosphorene for energy application
Authors: Hassani, Nasim; Yağmurcukardeş, Mehmet; Peeters, Francois M.; NeekAmal, Mehdi
Abstract: The influence of decoration with impurities and the composition dependent band gap in 2D materials has been the subject of debate for a long time. Here, by using Density Functional Theory (DFT) calculations, we systematically disclose physical properties of chlorinated phosphorene having the stoichiometry of PmCln. By analyzing the adsorption energy, charge density, migration energy barrier, structural, vibrational, and electronic properties of chlorinated phosphorene, we found that (I) the ClP bonds are strong with binding energy Eb =1.61 eV, decreases with increasing n. (II) Cl atoms on phosphorene have anionic feature, (III) the migration path of Cl on phosphorene is anisotropic with an energy barrier of 0.38 eV, (IV) the phonon band dispersion reveal that chlorinated phosphorenes are stable when r <= 0.25 where r = m/n, (V) chlorinated phosphorenes is found to be a photonic crystal in the frequency range of 280 cm1 to 325 cm1, (VI) electronic band structure of chlorinated phosphorenes exhibits quasiflat bands emerging around the Fermi level with widths in the range of 22 meV to 580 meV, and (VII) Cl adsorption causes a semiconducting to metallic/semimetallic transition which makes it suitable for application as an electroactive material. To elucidate this application, we investigated the change in binding energy (Eb), specific capacity, and opencircuit voltage as a function of the density of adsorbed Cl. The theoretical storage capacity of the chlorinated phosphorene is found to be 168.19 mA h g1with a large average voltage (similar to 2.08 V) which is ideal number as a cathode in chlorideion batteries.
20240101T00:00:00Z

Influence of high content of sodium doping in Bi(Pb)2212 superconductors
https://hdl.handle.net/11147/14029
Title: Influence of high content of sodium doping in Bi(Pb)2212 superconductors
Authors: Faiza, Bouaïcha; Mosbah, MohamedFayçal; Özyüzer, Lütfi
Abstract: Abstract: We study here, the effect of high content of sodium doping on structural and electrical properties of Bi(Pb)2212 superconductors. The Xray analysis results showed that all the prepared samples mainly belong to the superconducting tetragonal phase Bi–(Pb)2212. SEM micrographs show that the grains are closely related and have a characteristic flat shape for the superconductor Bi (Pb) 2212. For the undoped sample, the grains are randomly distributed with an average size of 5 μm. For doped samples, the morphology changes with sodium concentration. Resistivity measurements show that all samples have a superconducting character. © 2023, Pleiades Publishing, Ltd.
20230101T00:00:00Z

Photonic crystal textiles for heat insulation
https://hdl.handle.net/11147/14025
Title: Photonic crystal textiles for heat insulation
Authors: Çetin, Zebih; Tunçtürk, Yiğit; Sözüer, Hüseyin Sami
Abstract: In this work, we have studied transmission properties of a photonic crystallike structure that can be woven into fabrics. An interesting possibility emerges when considering the potential energy savings through suppression of radiation. It is a wellestablished fact that every object at a finite temperature inherently emits electromagnetic waves. Within the specific context of the human body, radiation takes on a crucial role as a fundamental mechanism governing heat dissipation. Thus, exploring ways to manage or mitigate this radiation could offer innovative approaches to optimize energy consumption and enhance heat regulation. It is well known that a photonic crystal can block electromagnetic energy with a specific frequency that is falling into a photonic bandgap. By using the numerical method called a finitedifference time domain, we have shown that this property of a periodic structure can be used to make textiles to save energy that is used to heat a human body environment. Numerical calculations have shown that by using the proposed photonic crystal structure, 53 % of electromagnetic energy is reflected. Although we mainly focused on textiles, it is worth highlighting that the same fundamental principle can be extended to diverse fields; for example, this structure can be integrated with construction materials and effectively function as a radiation heat insulator. © 2023 Author(s).
20230101T00:00:00Z