Controlling Nanoscale Thermal Expansion of Monolayer Transition Metal Dichalcogenides by Alloy Engineering

2D materials, such as transition metal dichalcogenides (TMDs), graphene, and boron nitride, are seen as promising materials for future high power/high frequency electronics. However, the large difference in the thermal expansion coefficient (TEC) between many of these 2D materials could impose a serious challenge for the design of monolayer‐material‐based nanodevices. To address this challenge, alloy engineering of TMDs is used to tailor their TECs. Here, in situ heating experiments in a scanning transmission electron microscope are combined with electron energy‐loss spectroscopy and first‐principles modeling of monolayer Mo_1?xW_xS₂ with different alloying concentrations to determine the TEC. Significant changes in the TEC are seen as a function of chemical composition in Mo_1?xW_xS₂, with the smallest TEC being reported for a configuration with the highest entropy. This study provides key insights into understanding the nanoscale phenomena that control TEC values of 2D materials.     

Quality-aware Wi-Fi offload: analysis,design and integration perspectives

The rapid spread of smart wireless devices and expansion of mobile data traffic have increased the interest for efficient traffic offloading techniques in next-generation communication technologies. Wi-Fi offloading uses ubiquitous Wi-Fi technology in order to satisfy the ever increasing demand for mobile bandwidth and therefore is an appropriate methodology for mobile operators. As a matter of fact, design and integration of an offloading technology inside mobile network operators’ infrastructures is a challenging task due to convergence issues between the The 3rd Generation Partnership Project (3GPP) and non-3GPP networks. Therefore, a connectivity management platform is a key element for integrated heterogeneous mobile network operators in order to enable smart and effective offloading. In this paper, analysis, design and integration of a connectivity management platform that uses a Multiple Attribute Decision Making (MADM) algorithm for efficient Wi-Fi Offloading in heterogeneous wireless networks is presented. In order to enhance the end-user’s quality-of-experience (QoE), we have especially concentrated on the benefits that can be achieved by exploiting the presence of integrated service provider platform. Hence, the proposed platform can collect several User Equipment (UE) and network-based attributes via infrastructure and client Application Programming Interfaces (APIs) and decides on the best network access technology (i.e. 3GPP and non-3GPP) to connect to for requested users. We have also proposed multi-user extensions of the MADM algorithms for offloading. Through simulations and experiments, we provide details of the comparisons of the proposed algorithms as well as the sensitivity analysis of the MADM algorithm through an experimental set-up.     

Structural,magnetic, electrical,and electrochemical properties of Sr–Co–Ru–O: A hybrid‐capacitor application

In this study, we report the synthesis of SrCo_1?xRu_xO_3?δ nominal compositions, where x = 0.0‐1.0, using solid‐state reaction technique. XRD analysis confirms the structure of x = 0 sample as hexagonal Sr₆Co₅O₁₅. As the Co ions are substituted by Ru, a two‐phase structure (hexagonal R32 and orthorhombic Pbnm) emerges up to x ≤ 0.5. As the Ru content is increased further, the hexagonal R32 phase disappears completely and an orthorhombic Pbnm phase becomes the main phase. SEM images show that grain size of the samples decreases with increasing Ru content. Temperature‐dependent electrical conductivity studies indicate upon Ru substitution in the nominal SrCo_1?xRu_xO_3?δ compounds, resistivity decreases due to appearance of metallic SrRuO₃ phase. The cyclic voltammogram (CV) of the samples show capacitive properties upon Ru substitution. The cycle measurements of the capacitors yield promising results for potential supercapacitor applications.     

Effects of cement type,water/cement ratio and cement content on sea water resistance of concrete

In this study, effects of cement type, cement content and water/cement (W/C) ratio level on the sea water resistance of concrete were investigated. Test samples were exposed to sea water by wetting–drying manner. Residual splitting tensile and compressive strength, and chloride penetration depths of specimens after exposure were determined. Besides, energy dispersive spectrometer (EDS) analyses were performed on scanning electron microscope (SEM) images of selected mixtures. Test results indicate that blast furnace slag cement (SC) mixtures have considerably greater resistance to sea water than portland cement (PC) mixtures both from the point of mechanical properties and chloride penetration.     

Site‐Specific Placement of Au Nanoparticles on Chemical Nanopatterns Prepared by Molecular Transfer Printing Using Block‐Copolymer Films

Inexpensive, large area patterning of ex‐situ synthesized metallic nanoparticles (NPs) at the nanoscale may enable many technologies including plasmonics, nanowire growth, and catalysis. Here, site‐specific localization of Au NPs onto nanoscale chemical patterns of polymer brushes is investigated. In this approach, patterns of hydroxyl‐terminated poly(styrene) brushes are transferred from poly(styrene‐block‐methyl methacrylate) (PS‐b‐PMMA) block copolymer films onto a replica substrate via molecular transfer printing, and the remaining areas are filled with hydroxyl‐terminated poly(2‐vinyl pyridine) (P2VP‐OH) brushes. Citrate‐stabilized Au NPs (13 nm) selectively bind to P2VP‐OH functionalized regions and the quality of the resulting assemblies depends on high chemical contrast in the patterned brushes. Minimization of the interpenetration of P2VP‐OH chains into PS brushes during processing is the key for achieving high chemical contrast. Large area hexagonal arrays of single Au NPs with a placement accuracy of 3.4 nm were obtained on patterns (～20 nm spots, ～40 nm pitch) derived from self‐assembled cylinder‐forming PS‐b‐PMMA films. Linear arrays of Au NPs were generated on patterns (40 nm lines, 80nm pitch) derived from lamellae‐forming PS‐b‐PMMA that had been directed to assemble on lithographically defined masters.     

Characterization of N, N′-bis-2-(1-hydoxy-4-methylpentyl)-3, 4, 9, 10-perylene bis (dicarboximide) sensitized nanocrystalline TiO2 solar cells with polythiophene hole conductors

We have fabricated solid-state, dye-sensitized nanocrystalline TiO₂ solar cells (DSSC) based on perylene derivative dye, N,N′-bis-2-(1-hydoxy-4-methylpentyl)-3,4,9,10-perylene bis (dicarboximide) (HMPER) with two different polythiophenes as hole conductors; i.e. poly (3-octyl thiophene) (P3OT) and poly (3-hexyl thiophene) (P3HT), respectively. HMPER adsorbs strongly to the surface of nanocrystalline TiO₂ and inject electrons into TiO₂ conduction band upon absorption of light. Polythiophene derivatives are well-known materials as hole conductors in solid-state dye-sensitized solar cells. We obtained quite similar results with P3OT and P3HT yielding a short-circuit current density of around 80 μA/cm² and open-circuit voltage of around 0.7 V at 80 mW/cm² AM 1.5 light intensity. The results are compared with Ru-535 TBA-sensitized nc-TiO₂ cells prepared by using the same polythiophene derivatives.     

A genetic algorithm based approach to vehicle routing problem with simultaneous pick-up and deliveries

The vehicle routing problem with simultaneous pick-up and deliveries, which considers simultaneous distribution and collection of goods to/from customers, is an extension of the capacitated vehicle routing problem. There are various real cases, where fleet of vehicles originated in a depot serves customers with pick-up and deliveries from/to their locations. Increasing importance of reverse logistics activities make it necessary to determine efficient and effective vehicle routes for simultaneous pick-up and delivery activities. The vehicle routing problem with simultaneous pick-up and deliveries is also NP-hard as a capacitated vehicle routing problem and this study proposes a genetic algorithm based approach to this problem. Computational example is presented with parameter settings in order to illustrate the proposed approach. Moreover, performance of the proposed approach is evaluated by solving several test problems.     

Effects of annealing on the structural and magnetic properties of flame spray pyrolyzed MnFe2O4 nanoparticles

In this study, manganese ferrite (MnFe₂O₄) nanoparticles were produced through flame spray pyrolysis (FSP). To investigate the effects of heat treatment, the nanoparticles were annealed between 400 and 650°C for 4 h in air in a comparative manner. The structural, chemical, morphological, and magnetic properties of the nanoparticles were evaluated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), dynamic light scattering (DLS), and vibrating sample magnetometry (VSM), respectively. The XRD results showed that the nanoparticles synthesized by the FSP method exhibited the MnFe₂O₄ spinel ferrite structure. The annealing process led to the decomposition of MnFe₂O₄ into various phases. According to the morphological analysis, the as-synthesized particles were hemispherical–cubic in shape and had an average particle size of less than 100 nm. In addition, the chemical bond structures of the nanoparticles were confirmed in detail by XPS elemental analysis. The highest saturation magnetization was recorded as 33.50 emu/g for the as-produced nanoparticles. The saturation magnetization of the nanoparticles decreased with increasing annealing temperature, while coercivity increased.