Scholarly Publications
http://hdl.handle.net/11693/102
Sun, 28 Feb 2021 06:15:25 GMT2021-02-28T06:15:25ZScholarly Publicationshttp://repository.bilkent.edu.tr:80/bitstream/id/6c98a91a-f201-475d-9acc-6e2b3d733bc0/
http://hdl.handle.net/11693/102
Core-crown quantum nanoplatelets with favorable type-II heterojunctions boost charge separation and photocatalytic NO oxidation on TiO2
http://hdl.handle.net/11693/75640
Core-crown quantum nanoplatelets with favorable type-II heterojunctions boost charge separation and photocatalytic NO oxidation on TiO2
Ebrahimi, Elnaz; İrfan, Muhammad; Shabani, Farzan; Koçak, Yusuf; Karakurt, Bartu; Erdem, E.; Demir, Hilmi Volkan; Özensoy, Emrah
Functionalization of TiO2 (P25) with oleic acid‐capped CdSe(core)/CdSeTe(crown) quantum‐well nanoplatelets (NPL) yielded remarkable activity and selectivity toward nitrate formation in photocatalytic NOx oxidation and storage (PHONOS) under both ultraviolet (UV‐A) and visible (VIS) light irradiation. In the NPL/P25 photocatalytic system, photocatalytic active sites responsible for the NO(g) photo‐oxidation and NO2 formation reside mostly on titania, while the main function of the NPL is associated with the photocatalytic conversion of the generated NO2 into the adsorbed NO3− species, significantly boosting selectivity toward NOx storage. Photocatalytic improvement in NOx oxidation and storage upon NPL functionalization of titania can also be associated with enhanced electron‐hole separation due to a favorable Type‐II heterojunction formation and photo‐induced electron transfer from the CdSeTe crown to the CdSe core of the quantum well system, where the trapped electrons in the CdSe core can later be transferred to titania. Re‐usability of NPL/P25 system was also demonstrated upon prolonged use of the photocatalyst, where NPL/P25 catalyst surpassed P25 benchmark in all tests.
Tue, 22 Sep 2020 00:00:00 GMThttp://hdl.handle.net/11693/756402020-09-22T00:00:00ZEnumerations of bargraphs with respect to corner statistics
http://hdl.handle.net/11693/75639
Enumerations of bargraphs with respect to corner statistics
Mansour, T.; Yıldırım, Gökhan
We study the enumeration of bargraphs with respect to some corner statistics. We find generating functions for the number of bargraphs that track the corner statistics of interest, the number of cells, and the number of columns. We also consider bargraph representation of set partitions and obtain some explicit formulas for the number of specific types of corners in such representations.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/11693/756392020-01-01T00:00:00ZFerroelectric based fractal phononic crystals: wave propagation and band structure
http://hdl.handle.net/11693/75638
Ferroelectric based fractal phononic crystals: wave propagation and band structure
Palaz, S.; Özer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
In this study, the band structure and transmission in multiferroic based Sierpinski carpet phononic crystal are investigated based on finite element simulation. In order to obtain the band structure of the phononic crystal (PnC), the Floquet periodicity conditions were applied to the sides of the unit cell. The square lattice PnC consists of various piezoelectric inclusion in a rubber matrix with square and circular cross section.
Wed, 01 Apr 2020 00:00:00 GMThttp://hdl.handle.net/11693/756382020-04-01T00:00:00ZElastic and optical properties of sillenites: First principle calculations
http://hdl.handle.net/11693/75637
Elastic and optical properties of sillenites: First principle calculations
Koç, H.; Palaz, S.; Şimşek, Ş.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present paper, we have investigated the electronic structure of some sillenites - Bi12MO20 (M = Ti, Ge, and Si) compounds based on the density functional theory. The mechanical and optical properties of Bi12MO20 have also been computed. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The band gap trend in Bi12MO20 can be understood from the nature of their electronic structures. The obtained electronic band structure for all Bi12MO20 compounds is semiconductor in nature. Similar to other oxides, there is a pronounced hybridization of electronic states between M-site cations and anions in Bi12MO20. Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions.
Wed, 01 Apr 2020 00:00:00 GMThttp://hdl.handle.net/11693/756372020-04-01T00:00:00ZComplete photonic band gaps in Sn2P2X6 (X = S, Se) supercell photonic crystals
http://hdl.handle.net/11693/75636
Complete photonic band gaps in Sn2P2X6 (X = S, Se) supercell photonic crystals
Şimşek, Ş.; Palaz, S.; Koç, H.; Mamedov, Amirullah M.; Özbay, Ekmel
In this work, we present an investigation of the optical properties and band structures for the photonic crystal structures (PCs) based on Sn2P2X6: X = S, Se) with Fibonacci superlattices. The optical properties of PCs can be tuned by varying structure parameters such as the lengths of poled domains, filling factor, and dispersion relation. In our simulation, we employed the finite-difference time domain technique and the plane wave expansion method, which implies the solution of Maxwell equations with centered finite-difference expressions for the space and time derivatives.
Wed, 01 Apr 2020 00:00:00 GMThttp://hdl.handle.net/11693/756362020-04-01T00:00:00ZBaTiO3 based photonic time crystal and momentum stop band
http://hdl.handle.net/11693/75635
BaTiO3 based photonic time crystal and momentum stop band
Özer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
Temporally periodic photonic crystals develop an ω-k dispersion relation with momentum band gaps. While conventional photonic crystals induce forbidden bands in the frequency spectrum of photons, photonic time crystals create forbidden regions in the momentum spectrum of photons. This effect allows for enhanced control over many optical processes that require both photonic energy and momentum conservations such as nonlinear harmonic generation. The simulation results show that more intensive scatter fields can obtained in photonic space time crystal. Also, we investigate topological phase transitions of photonic time crystals systems.
Wed, 01 Apr 2020 00:00:00 GMThttp://hdl.handle.net/11693/756352020-04-01T00:00:00ZFLRW-cosmology in generic gravity theories
http://hdl.handle.net/11693/75634
FLRW-cosmology in generic gravity theories
Gürses, Metin; Heydarzade, Yaghoub
We prove that for the Friedmann–Lemaitre–Robertson–Walker metric, the field equations of any generic gravity theory in arbitrary dimensions are of the perfect fluid type. The cases of general Lovelock and F(R,G)F(R,G) theories are given as examples.
Sun, 01 Nov 2020 00:00:00 GMThttp://hdl.handle.net/11693/756342020-11-01T00:00:00ZD-bound and the Bekenstein bound for the surrounded Vaidya black hole
http://hdl.handle.net/11693/75633
D-bound and the Bekenstein bound for the surrounded Vaidya black hole
Hadi, H.; Darabi, F.; Atazadeh, K.; Heydarzade, Yaghoub
We study the Vaidya black hole surrounded by the exotic quintessence-like, phantom-like and cosmological constant-like fields by means of entropic considerations. Explicitly, we show that for this thermodynamical system, the requirement of the identification of the D-bound and Bekenstein entropy bound can be considered as a thermodynamical criterion by which one can rule out the quintessence-like and phantom-like fields, and prefer the cosmological constant as a viable cosmological field.
Sun, 01 Nov 2020 00:00:00 GMThttp://hdl.handle.net/11693/756332020-11-01T00:00:00ZThe computational framework for continuum-kinematics-inspired peridynamics
http://hdl.handle.net/11693/75632
The computational framework for continuum-kinematics-inspired peridynamics
Javili, Ali; Firooz, Soheil; McBride, A. T.; Steinmann, P.
Peridynamics (PD) is a non-local continuum formulation. The original version of PD was restricted to bond-based interactions. Bond-based PD is geometrically exact and its kinematics are similar to classical continuum mechanics (CCM). However, it cannot capture the Poisson effect correctly. This shortcoming was addressed via state-based PD, but the kinematics are not accurately preserved. Continuum-kinematics-inspired peridynamics (CPD) provides a geometrically exact framework whose underlying kinematics coincide with that of CCM and captures the Poisson effect correctly. In CPD, one distinguishes between one-, two- and three-neighbour interactions. One-neighbour interactions are equivalent to the bond-based interactions of the original PD formalism. However, two- and three-neighbour interactions are fundamentally different from state-based interactions as the basic elements of continuum kinematics are preserved precisely. The objective of this contribution is to elaborate on computational aspects of CPD and present detailed derivations that are essential for its implementation. Key features of the resulting computational CPD are elucidated via a series of numerical examples. These include three-dimensional problems at large deformations. The proposed strategy is robust and the quadratic rate of convergence associated with the Newton–Raphson scheme is observed.
Wed, 01 Jul 2020 00:00:00 GMThttp://hdl.handle.net/11693/756322020-07-01T00:00:00ZOn the absence of stability of bases in some Fréchet spaces
http://hdl.handle.net/11693/75631
On the absence of stability of bases in some Fréchet spaces
Goncharov, Alexander
We show that, for each compact subset of the real line of infinite cardinality with an isolated point, the space of Whitney jets on the set does not possess a basis consisting only of polynomials. On the other hand, polynomials are dense in any Whitney space. Thus, there are no general results about stability of bases in Fréchet spaces.
Sat, 01 Aug 2020 00:00:00 GMThttp://hdl.handle.net/11693/756312020-08-01T00:00:00Z