Robustness of One-Dimensional Photonic Bandgaps Under Random Variations of Geometrical Parameters

The supercell method is used to study the variation of the photonic bandgaps in one-dimensional photonic crystals under random perturbations to thicknesses of the layers. The results of both plane wave and analytical band structure and density of states calculations are presented along with the transmission cofficient as the level of randomness and the supercell size is increased. It is found that higher bandgaps disappear first as the randomness is gradually increased. The lowest bandgap is found to persist up to a randomness level of 55 percent.Comment: Submitted to Physical Review B on April 8 200

Utilization of Boron Waste Borogypsum with Silica Fume as a Supplementary Cementitious Material in Mortar

In the current study, borogypsum and borogypsum with silica fume mixtures are added to cement clinker partially. Flexural tensile strength, compressive strength and water absorption tests are performed on mortar samples which contain borogypsum and silica fume and also high temperature effect on the mortars are investigated. As a result of the tests it is revealed that 5% addition of borogysum and borogypsum-silica fume mixtures to cement clinker are altered strength behaviors of the mortars

Speciational view of macroevolution: are micro and macroevolution decoupled?

We introduce a simple computational model that, with a microscopic dynamics driven by natural selection and mutation alone, allows the description of true speciation events. A statistical analysis of the so generated evolutionary tree captures realistic features showing power laws for frequency distributions in time and size. Albeit these successful predictions, the difficulty in obtaining punctuated dynamics with mass extinctions suggests the necessity of decoupling micro and macro-evolutionary mechanisms in agreement with some ideas of Gould's and Eldredge's theory of punctuated equilibrium.Comment: Europhys. Lett. 75:342--34

Thermally Curable Polybutadiens By Ckick Reactions

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2008Bu çalışmada polibutadienin uygun koşullarda bromlanarak aizdleme reaksiyonuna hazır hale getirilip, polibutadienazid elde edilerek klik kimyası uygulanarak propargilbenzoksazin fonksiyonlarının polybutadiene bağlanarak halka kapanması reaksiyonlarının gerçekleştirilmesi ve böylece yüksek oranlarda ısıya dayanıklı özellikteki polimerlerin elde edilmesi amaçlanmaktadır. Bu yöntemle azidleme ve klik reaksiyonu sonucunda polibutadienin mekanik özelliklerindeki değişimler ve avantajları incelenecektir.Spektral ve termal analizler sentezlenen polimerde benzoksazin fonksiyonunun varlığını ispat etmişlerdir.Benzoksazin çeren polibutadienin termal olarak aktiflenip kataliz olmaksızın sertleştirilebilir olduğu gösterilmiş ve sertleştirilme sonrasında char eldesi olduğu gözlenmiştir. Sentezlenen polimerlerin molekül ağırlıkları ile polidisperistelerinin belirlenmesinde GPC kullanılacaktır.In this thesis, novel side-chain benzoxazine functional polybutadiene (PB-Benzoxazine) was synthesized by using “Click Chemistry” strategy. First, approximately 10% of double bonds were brominated with Br2 in CCl4 then these bromo groups converted to azido groups by using NaN3 in DMF. Propargyl benzoxazine was prepared independently by a ring closure reaction between p-propargyloxy aniline, paraformaldehyde and phenol. Finally, azidofunctionalized PB was coupled to propargyl benzoxazine with high efficiency by click chemistry. The spectral and thermal analysis confirmed the presence of benzoxazine functionality in the resulting polymer. It is shown that PB containing benzoxazine undergoes thermally activated curing in the absence of any catalyst forming PB thermoset with high char yield.Yüksek LisansM.Sc

Utilization of Colemanite waste in Concrete Design

Waste material is formed in enormous quantities during the beneficiation of raw ore. These wastes can cause both economic loss and environmental pollution. Thus, in this study, the effect of CW obtained from Eti Mine Establishments Kütahya-Emet Boron Plants on the compressive strength and cylinder splitting tensile strength of concrete and its USAbility as a concrete admixture is investigated. The results found show that utilization of Colemanite Waste is possible when it is used as additive in concrete

Effect of carbon support on the activity of monodisperse Co45Pt55 nanoparticles for oxygen evolution in alkaline media

Oxygen evolution reaction (OER) represents the efficiency-limiting reaction in water electrolyzers, metal-air batteries, and unitized regenerative fuel cells. To achieve high-efficiency OER in alkaline media, we fabricated three novel electrocatalysts by the assembly of as-prepared Co45Pt55 alloy nanoparticles (NPs) on three different carbon-based support materials: reduced graphene oxide (CoPt/rGO), mesoporous graphitic carbon nitride (CoPt/mpg-CN), and commercial Ketjenblack carbon (CoPt/KB). Voltammetry studies revealed that CoPt/rGO electrocatalyst provided lower OER overpotentials accompanied by higher currents and specific current density values than the other two studied materials. Moreover, CoPt/rGO outperformed commercial CoPt/C electrocatalysts in terms of notably higher specific current densities. Additionally, it was found that CoPt/rGO electrocatalyst activity increases with increasing temperature up to 85°C, as suggested by the increase in the exchange current density. Electrochemical impedance spectroscopy studies of three electrocatalysts in OER revealed similar charge transfer resistance, although CoPt/rGO provided a higher current density. The main issue observed during long-term chronoamperometry and chronopotentiometry studies is the materials’ instability under OER polarization conditions, which is still to be tackled in future work

Heteroleptic coordination environments in metal-mediated DNA G-quadruplexes

The presence of metal centers with often highly conserved coordination environments is crucial for roughly half of all proteins, having structural, regulatory, or enzymatic function. To understand and mimic the function of metallo-enzymes, bioinorganic chemists pursue the challenge of synthesizing model compounds with well-defined, often heteroleptic metal sites. Recently, we reported the design of tailored homoleptic coordination environments for various transition metal cations based on unimolecular DNA G-quadruplex structures, templating the regioselective positioning of imidazole ligandosides LI. Here, we expand this modular system to more complex, heteroleptic coordination environments by combining LI with a new benzoate ligandoside LB within the same oligonucleotide. The modifications still allow the correct folding of parallel tetramolecular and antiparallel unimolecular G-quadruplexes. Interestingly, the incorporation of LB results in strong destabilization expressed in lower thermal denaturation temperatures Tm. While no transition metal cations could be bound by G-quadruplexes containing only LB, heteroleptic derivatives containing both LI and LB were found to complex CuII, NiII, and ZnII. Especially in case of CuII we found strong stabilizations of up to ΔTm = +34°C. The here shown system represents an important step toward the design of more complex coordination environments inside DNA scaffolds, promising to culminate in the preparation of functional metallo-DNAzymes