Enhanced oxidation resistance of magnesium nanorods grown by glancing angle deposition

Oxidation behavior of magnesium thin films and nanorods were investigated in the temperature range of 25-550 °C by using thermal gravimetric analysis. Arrays of vertical magnesium nanorods were deposited by the DC magnetron sputtering glancing angle deposition technique, while the magnesium thin films were deposited using the same system but at normal incidence. The morphologies and corresponding crystal structure of the samples were analyzed by scanning electron microscopy, transmission electron microscopy and X-ray diffraction methods, respectively. We report that the Mg thin films showed oxidation induced weight gain starting from room temperature. On the other hand, Mg nanorods did not show any indication of significant oxidation at temperatures below 350 °C. Enhanced oxidation resistance of Mg nanorods was also confirmed by quartz crystal microbalance measurements. At temperatures higher than 350 °C, Mg nanorods started to get oxidized and their weight increased at a similar rate to that of Mg thin films. We argue that reduced oxidation of Mg nanorods is mainly attributed to their single crystal nature. Magnesium nanorods’ reduced oxidation can potentially play a key role in hydrogen storage and gas sensing applications.     

Influence of Fly Ash on the Properties of Asphalt

Abstract

In this study, we investigated fly ash replacement of the fine aggregate in hot-mix asphalt concrete mixtures. Fly ash was obtained from the Soma thermal power plant. Fly ash in amounts of 5, 6, 7, and 8% by total aggregate weight was added as an additive to asphalt concrete mixtures. Mixtures were prepared without additives containing filler, which had the same percentages as the fly ash mixtures, and briquette samples were prepared from mixtures with fly ash and with filler. Marshall tests were applied to the samples, and optimum asphalt contents were determined. In the optimum conditions, parameters were determined, which were stability, practical specific gravity, void, flow, and max theoretical specific gravity. The results indicate that the stability values obtained from mixtures with fly ash are higher than mixtures from filler. The highest stability value was obtained from 5% fly ash added mixture, which was 1,630 kg in optimal conditions.     

Dwell time and average dwell time methods based on the cycle ratio of the switching graph

A new method to find an upper bound on dwell time and average dwell time for switched linear systems is proposed. The method is based on computing the maximum cycle ratio and the maximum cycle mean of the directed graph that governs switchings. For planar switched systems, an upper bound for dwell time and average dwell time can be estimated by considering only the cycles of length two.     

HYDRODYNAMIC STUDIES IN A HALF SLOT-RECTANGULAR SPOUTED BED COLUMN

Experiments were carried out in a half slot-rectangular spouted bed to investigate the effects of slot width and lower section basal angle on column hydrodynamics. Flow regimes, minimum spouting velocity, spouting and maximum pressure drops, and maximum spoutable bed height were determined for 4?mm diameter polyethylene particles. The results are compared with those for conventional cylindrical and rectangular spouted beds. Correlations for each hydrodynamic parameter are developed and compared with equations available in the literature.     

Effects of Different Fin Spacings on the Nusselt Number and Reynolds Number in Perforated Finned Heat Exchangers

In this study, the effect of holes placed on perforated finned heat exchangers on convective heat transfer was experimentally investigated. Six-millimeter-diameter holes were opened on each circular fin on a heating tube in order to increase convective heat transfer. These holes were placed on the circular fins in such a way as to follow each other at the same chosen angle. The holes created turbulence in a region near the heating tube surface on the bottom of the fin. Experiments were then performed to analyze the effect of this turbulence on heat transfer and pressure drop. These experiments were carried out at five different fin spacings at the angular locations of 30° and 60° in order to determine the optimum fin spacing. Moreover, further experiments were carried out for counterflow and parallel-flow arrangements to determine the effects of the flow directions of the heating fluid and heated fluid. Results show an increase in Nusselt number with increasing modified Reynolds number. In addition, when different fin spacing to heating tube external diameter ratios were examined, at a ratio of 0.414 and angular locations of 30° and 60°, 11% and 8.6% increase in heat transfer were obtained, respectively, for parallel-flow arrangement compared to counterflow. For parallel flow, pressure drop values were 3.5% and 3.8% lower at 30° and 60°, respectively.     

Drying Behavior of Meat Samples at Various Fiber Directions and Air Conditions

The aim of this study was to investigate the effects of meat fiber directions and air conditions on moisture and temperature developments, shrinkage, and effective diffusivity constants compared to homogenous minced meat samples. The lean meat with three fiber directions and minced meat samples were dried at temperatures of 48 and 70°C and air flow rates of 0.5, 1.0, and 1.7 m/s. The minced meat samples showed 1.0 ± 0.19 to 4.4 ± 0.03°C higher temperature values and 2.3 ± 0.004 to 6.2 ± 0.003% lower moisture losses than the lean meat samples in all fiber directions. The lowest temperatures were observed in lean meat with h ₁ (normal flow, normal drying) fiber direction. The highest moisture loss and diffusion coefficient were observed in lean meat with h ₂ (parallel flow, normal drying) and v (normal flow, parallel drying) fiber directions, which also possessed the shortest drying times (10.4 and 13.4 h, respectively). The estimated diffusion coefficient values ranged between 1.11 × 10^?9 and 5.54 × 10^?9. The results indicated that lean and minced meat samples differed in their drying behaviors in a tray dryer under the tested conditions with >90% reproducibility (or ≤10% coefficient of variation).     

Effect of Shell Coating Techniques on Dynamic Response of Photoconductive Core/Shell Nanorod Arrays

Efficient carrier collection in the core/shell nanowire (nanorod) arrays requires a high quality interface between core and shell materials. A highly conformal shell layer around nanorods can lead to fast dynamic response in photoconductive devices by a radial charge flow. Therefore, choice of the deposition technique for the conformal shell layer becomes crucial. In this study, the dynamic response of indium sulfide (In₂S₃) nanorods/silver (Ag) core/shell devices is compared in which Ag shell layers are deposited by different physical vapor deposition (PVD) techniques. In₂S₃ nanorods are fabricated by glancing angle deposition. The core/shell devices with Ag shell sputtered at a relatively high working gas pressure (≈3 × 10⁻² mbar) produce the highest photocurrent compared to other devices in which more directional incident flux (with working gas pressure of ≈3 × 10⁻³ mbar) is utilized for Ag shell layer. The reduced transit times indicate a conformal shell achieved by the high pressure sputtering technique that has a wide angular distribution flux. In addition, a more directional flux yet with a small angle (≈30°) incidence with respect to the substrate surface normal also helps increase the photocurrent. Such simple and scalable PVD techniques are shown to offer alternative fabrication approaches in producing high quality core/shell nanostructures.     

Silicon and Chlorine Substituted Unsaturated Polymers: ROMP of (bicyclo[2,2,1]hept-5-en-2-yl)ethylchlorodimethylsilane via Mo-based catalyst

Ring opening metathesis polymerization (ROMP) of a norbornene derivative that contains silicon and chlorine, (bicyclo[2,2,1]hept-5-en-2-yl)ethylchlorodimethylsilane, by using electrochemically produced active catalyst species (MoCl₅–e⁻–Al–CH₂Cl₂) was investigated. Silicon and chlorine containing unsaturated polymer was characterized by ¹H, ¹³C, and ²⁹Si-NMR and FTIR spectroscopy. The thermal behavior of the polymer was determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).     

From the knitting shop: the first physical and dynamic model of the taenioglossan radula (Mollusca: Gastropoda) aids in unravelling functional principles of the radular morphology

The radula is the structure used for food processing in Mollusca. It can consist of a membrane with stiffer teeth, which is, together with alary processus, muscles and odontophoral cartilages, part of the buccal mass. In malacology, it is common practice to infer potential tooth functions from morphology. Thus, past approaches to explain functional principles are mainly hypothesis driven. Therefore, there is an urgent need for a workflow testing hypotheses on the function of teeth and buccal mass components and interaction of structures, which can contribute to understanding the structure as a whole. Here, in a non-conventional approach, we introduce a physical and dynamic radular model, based on morphological data of Spekia zonata (Gastropoda, Paludomidae). Structures were documented, computer-modelled, three-dimensional-printed and assembled to gather a simplistic but realistic physical and dynamic radular model. Such a bioinspired design enabled studying of radular kinematics and interaction of parts when underlain supporting structures were manipulated in a similar manner as could result from muscle contractions. The presented work is a first step to provide a constructional manual, paving the way for even more realistic physical radular models, which could be used for understanding radular functional morphology and for the development of novel gripping devices.