Assessment of the Thermal Conductivity of BN-C Nanostructures

Chemical and structural diversity present in hexagonal boron nitride ((h-BN) and graphene hybrid nanostructures provide new avenues for tuning various properties for their technological applications. In this paper we investigate the variation of thermal conductivity ($\kappa$) of hybrid graphene/h-BN nanostructures: stripe superlattices and BN (graphene) dots embedded in graphene (BN) are investigated using equilibrium molecular dynamics. To simulate these systems, we have parameterized a Tersoff type interaction potential to reproduce the ab initio energetics of the B-C and N-C bonds for studying the various interfaces that emerge in these hybrid nanostructures. We demonstrate that both the details of the interface, including energetic stability and shape, as well as the spacing of the interfaces in the material exert strong control on the thermal conductivity of these systems. For stripe superlattices, we find that zigzag configured interfaces produce a higher $\kappa$ in the direction parallel to the interface than the armchair configuration, while the perpendicular conductivity is less prone to the details of the interface and is limited by the $\kappa$ of h-BN. Additionally, the embedded dot structures, having mixed zigzag and armchair interfaces, affects the thermal transport properties more strongly than superlattices. Though dot radius appears to have little effect on the magnitude of reduction, we find that dot concentration (50% yielding the greatest reduction) and composition (embedded graphene dots showing larger reduction that h-BN dot) have a significant effect

On Calculation of Thermal Conductivity from Einstein Relation in Equilibrium MD

In equilibrium molecular dynamics, Einstein relation can be used to calculate the thermal conductivity. This method is equivalent to Green-Kubo relation and it does not require a derivation of an analytical form for the heat current. However, it is not commonly used as Green-Kubo relationship. Its wide use is hindered by the lack of a proper definition for integrated heat current (energy moment) under periodic boundary conditions. In this paper, we developed an appropriate definition for integrated heat current to calculate thermal conductivity of solids under periodic conditions. We applied this method to solid argon and silicon based systems; compared and contrasted with the Green-Kubo approach.Comment: We updated this manuscript from second version by changing the title and abstract. This paper is submitted to J. Chem. Phy

Equilibrium Limit of Boundary Scattering in Carbon Nanostructures: Molecular Dynamics Calculations of Thermal Transport

It is widely known that graphene and many of its derivative nanostructures have exceedingly high reported thermal conductivities (up to 4000 W/mK at 300 K). Such attractive thermal properties beg the use of these structures in practical devices; however, to implement these materials while preserving transport quality, the influence of structure on thermal conductivity should be thoroughly understood. For graphene nanostructures, having average phonon mean free paths on the order of one micron, a primary concern is how size influences the potential for heat conduction. To investigate this, we employ a novel technique to evaluate the lattice thermal conductivity from the Green-Kubo relations and equilibrium molecular dynamics in systems where phonon-boundary scattering dominates heat flow. Specifically, the thermal conductivities of graphene nanoribbons and carbon nanotubes are calculated in sizes up to 3 microns, and the relative influence of boundary scattering on thermal transport is determined to be dominant at sizes less than 1 micron, after which the thermal transport largely depends on the quality of the nanostructure interface. The method is also extended to carbon nanostructures (fullerenes) where phonon confinement, as opposed to boundary scattering, dominates, and general trends related to the influence of curvature on thermal transport in these materials are discussed

Microstructural defect properties of InGaN/GaN blue light emitting diode structures

Cataloged from PDF version of article.In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current-voltage characteristic (I-V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I-V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure's structural, optical and electrical results supported one another

Üç Tritikale Çeşidinde Verim ve Verim Komponentleri İçin Kuraklığa Dayanım İndekslerinin Değerlendirilmesi

Drought is a wide-spread problem seriously influencing cereal production and quality. The development of triticale cultivars which are tolerant to drought is an objective in many breeding programmes, but so far success has been limited. This study was carried to examine differences in yield and yield components and kernel features among triticale cultivars (Tatlicak 97, Karma 2000 and MIKHAM 2002) under drought stress. Three triticale cultivars with different yield performance were grown in separate experiments under the rain fed and irrigated conditions at Eskisehir, Turkey, in 2006-2007 growing season. In the study, susceptibility index (SSI), stress tolerance index (STI), tolerance (TOL), yield index (YI), yield stability index (YSI), mean productivity (MP) and geometric mean productivity (GMP) were calculated. The best yielding cultivar under the drought stress, hence having a low susceptibility index, was Karma 2000. This cultivar may be utilized for improvement of drought resistance in triticale breeding programmes.Kuraklık, tahıl üretimi ve kalitesini ciddi şekilde etkileyen yaygın bir problemdir. Kuraklığa toleranslı tritikale çeşitlerinin geliştirilmesi pek çok ıslah programının amacıdır fakat bugüne kadarki başarı sınırlı kalmıştır. Bu çalışma, kuraklık stresi altında verim, verim ögeleri ve tane özellikleri bakımından tritikale çeşitleri (Tatlicak 97, Karma 2000 and MIKHAM 2002) arasındaki farklılıkları incelemek amacıyla yürütülmüştür. Verim performansları farklı üç tritikale çeşidi 2006–2007 üretim sezonunda, Eskişehir, Türkiye’de sulu ve kuru koşullar altında farklı denemelerde yetiştirilmiştir. Çalışmada, stres duyarlılık indeksi (SSI), stres tolerans indeksi (STI), tolerans (TOL), verim indeksi (YI), verim stabilite indeksi (YSI), ortalama verimlilik (MP) ve geometrik ortalama verimlilik (GMP) indeksleri hesaplanmıştır. Kuraklık stresi altında en iyi verime sahip olan çeşit, en düşük duyarlılık indeksine sahip olmasına karşılık Karma 2000’dir. Bu çeşit, tritikalede kuraklığa dayanımı geliştirmek için ıslah programlarında kullanılabilir

A COMPUTATIONAL HYDRODYNAMIC ANALYSIS OF DUISBURG TEST CASE WITH FREE SURFACE AND PROPELLER

This paper discusses the effects of the free surface and the propeller on a benchmark Post-Panamax Ship, Duisburg Test Case (DTC). The experimental results are already available in the literature. The computational study carried out in this work is verified first with the experiments and then used to explain some of the physical aspects associated with viscous ship flows. There are two interesting outcomes of this work. The first one is, the existence of the propeller contributes to the pressure resistance of the ship by increasing the wave elevations along the hull and the fluid domain substantially. The second outcome is; by changing the pressure distribution along the hull and the propeller, the free surface increases the efficiency of the propulsion system. These specific outcomes are thoroughly discussed in the paper with CFD generated results and physical explanations

A COMPUTATIONAL HYDRODYNAMIC ANALYSIS OF DUISBURG TEST CASE WITH FREE SURFACE AND PROPELLER

This paper discusses the effects of the free surface and the propeller on a benchmark Post-Panamax Ship, Duisburg Test Case (DTC). The experimental results are already available in the literature. The computational study carried out in this work is verified first with the experiments and then used to explain some of the physical aspects associated with viscous ship flows. There are two interesting outcomes of this work. The first one is, the existence of the propeller contributes to the pressure resistance of the ship by increasing the wave elevations along the hull and the fluid domain substantially. The second outcome is; by changing the pressure distribution along the hull and the propeller, the free surface increases the efficiency of the propulsion system. These specific outcomes are thoroughly discussed in the paper with CFD generated results and physical explanations

Assessing and minimizing the risk of cerebrospinal fluid leakage after intradural surgery

This thesis evaluated the effectiveness of current sealants in preventing incisional CSF leakage. Subsequently, we developed a new dural sealant patch (Liqoseal) which should ultimately prevent incisional CSF leakage in patients. However, before clinical application, the effectiveness and the safety of this sealant in preclinical studies had to be evaluated. In this thesis the in vitro effectiveness and in vivo safety of Liqoseal have been studied

Modelling of chemical reactions in metallurgical processes

Since the last three decades, the study of reduction of iron-ore has gained much attention as it is considered a core process for the steel industry. Fluidized bed and moving bed reactors are utilized to reduce the iron-ore efficiently. As reducing agents coal, coke or natural gases are used, which are released as CO2 gas, or sometimes in small amounts as H2O to the environment. The conditions in these reactors are harsh and provide limited accessibility, therefore computational tools are used to investigate them. One such tool is the CFD-DEM method, where the reacting gas species and the governing equations for the gas flow are calculated in the Eulerian (CFD) side, whereas the particle reactions and equation of motion are calculated in the Lagrangian (DEM) side. In the current work, the CFD-DEM method is extended to cover the most dominant types of models for heterogeneous reactions between submerged solids and fluids. One of these models is the Shrinking Particle Model (SPM), which is used to verify the commu- nication framework between the CFD and DEM sides by running preliminary test cases. Another model is the Unreacted Shrinking Core Model (USCM), which is considered as a good model for a reality like iron-ore reduction modelling