Characterization of iron oxide thin films prepared by sol-gel processing

Iron oxide thin films were prepared by spin-coating a gel solution of iron(III) nitrate dissolved in 2-methoxyethanol and acetylacetone on glass and quartz substrates. The film thickness was adjusted by changing the spinning rate of the spin coater. Annealing was carried out between 300 degrees C to 600 degrees C to investigate the phases present in the films. Viscosity of the main solution was found as 0.0035 Pa.s by viscosity measurement. TGA/DTA analyses showed that heat treatment should be done between 330 degrees C and 440 degrees C in order to produce maghemite thin films. SEM studies showed that single layer thickness of the films were between 65 and 80 nm. The structural characteristics were evaluated by changing the experimental parameters which are annealing temperature, annealing time and thickness of the films. From the X-ray diffraction analysis, maghemite formation was observed with decreasing annealing temperature, annealing time and film thickness. TEM results verified the presence of the maghemite phase by electron diffraction and selected area electron diffraction (SAED) methods. According to UV-Vis results transmittance of the films decreases with increasing annealing temperature.     

Advanced energy‐based analyses of trusses employing hybrid metaheuristics

Total potential optimization using metaheuristic algorithm (TPO/MA) is an alternative method in structural analyses, and it is a black‐box application for nonlinear analyses. In the study, an advanced TPO/MA using hybridization of several metaheuristic algorithms is investigated to solve large‐scale structural analyses problems. The new generation algorithms considered in the study are flower pollination algorithm (FPA), teaching learning‐based optimization, and Jaya algorithm (JA). Also, the proposed methods are compared with methodologies using classic and previously used algorithms such as differential evaluation, particle swarm optimization, and harmony search. Numerical investigations were carried out for structures with four to 150 degrees of freedoms (design variables). It has been seen that in several runs, JA gets trapped into local solutions. For that reason, four different hybrid algorithms using fundamentals of JA and phases of other algorithms, namely, JA using Lévy flights, JA using Lévy flights and linear distribution, JA with consequent student phase, and JA with probabilistic student phase (JA1SP), are developed. It is observed that among the variants tried, JA1SP is seen to be more effective on approaching to the global optimum without getting trapped in a local solution.     

The Effects of Sb Substitution on Structural Properties in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> Superconductors

In this study, the effects of partial Sb³⁺ ion substitutions for the Y sites and the Cu sites on the superconducting properties of YBa₂Cu₃O _y (Y123) ceramic superconductors were investigated. The samples were prepared by the conventional solid-state reaction method and the properties of the samples were investigated by means of X-ray diffraction, AC magnetic susceptibility measurements, scanning electron microscope, and energy dispersive X-ray analysis. The critical temperatures were determined to be in the range of 80–92 K for both Systems I and II. It was found that Sb-addition leads to the formation of the non-superconducting YBa₂SbO₆ phase, which has a negative effect on the critical temperature, since the highest critical temperature was measured for pure Y123. However, the increasing substitution level has a negligible effect on the X-ray diffraction analysis peak intensities of the superconducting phases. In addition, SEM images showed that Sb substitution decreases the grain size and modifies the microstructure development, which makes the samples denser.     

Dependence of the Structural, Electrical and Magnetic Properties of YBa2Cu3O7?δ Bulk Superconductor on the Ag Doping

The effects of Ag dopants on the superconducting properties of YBCO bulk samples, prepared under solid-state reaction method, have been studied by resistivity?Ctemperature (???CT), X-ray diffraction (XRD), scanning electron microscope (SEM), bulk density, AC susceptibility, DC magnetization measurements, and theoretical analysis. Small Ag substitutions (x??0.10) do not effect T _c of pure YBa₂Cu_3?x Ag _x O_7??? , while we observed small decreases of 1.5?K for larger doping levels (x??0.15). AC susceptibility measurements for sintered YBCO pellets have been performed as a function of temperatures at constant frequency and AC field amplitude in the absence of DC bias field. The critical current densities (J _c ) have been estimated as a function of magnetic field from the magnetization data employing Bean??s critical state model. The increase in Ag amount (x) in YBa₂Cu_3?x Ag _x O_7??? (x??0.10) system effectively decreases the intragrain critical current density, which is attributed to the reduced connectivity between the grain boundaries. In the case of small additions (x=0.05), Ag atoms fill partly the pores, leading better crystallization of the grains.     

Molecular dynamics simulations on constraint metal binding peptides

Molecular dynamics (MD) simulations are performed using constraint polypeptides that were combinatorially selected to have binding affinities for the noble metal platinum (Pt). We analyzed the effects of the threonine-serine-threonine (T-S-T) amino acid sequence because this domain is common among strong binders. Using pair correlation functions, intermolecular interactions are evaluated between peptide residues and the metal surface in the presence of solvent water. In explicit simulations in the absence of metal surface, we find that among the experimentally verified strong binders the side chain groups within the T-S-T region make hydrogen bonding with water molecules, i.e. being more solvent exposed. In MD simulations including the metal, the T-S-T region interacts with the substrate to an extent greater than those with the non-polar residues. However, it is also observed that carbonyl and amide groups on the backbone and certain residues, such as Arg and Pro, also exhibit close interactions with the surface. Backbone torsional angle auto-correlation functions indicate that threonine and serine residues impart the highest flexibility to the backbone of the chains in solvent simulations in the absence of the surface. This flexibility of the peptides and their interactions with the metal surface are major players in binding. The simulations also reveal that the flexibility of the whole chain is considerably hindered upon binding. These results have significant implications in understanding of how constraint peptides selectively bind to a metal surface and may provide insight into the design of new sequences.     

Synthesis of tin oxide-coated gold nanostars and evaluation of their surface-enhanced Raman scattering activities

Tin oxide-coated gold nanostar hybrid nanostructures are prepared by first synthesizing gold nanostars (ca. 400 nm), then introducing Na₂SnO₃ precursor followed by its hydrolysis and formation of a tin oxide layer on nanoparticle surface. The synthesized hybrid structures have been characterized by combination of UV–Vis spectroscopy, transmission electron microscope (TEM), energy-dispersive X-ray studies, scanning electron microscope (SEM), X-Ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The TEM and SEM analyses showed that gold nanostars have a coating with an approximate thickness of 15 nm. The tin (IV) oxide coating on the gold nanostars was identified by XRD and XPS analyses and confirmed by FTIR spectroscopy. Surface-enhanced Raman scattering (SERS) spectroscopy was performed on tin oxide-coated and uncoated gold nanostars with crystal violet as a probe molecule. The SERS studies revealed field enhancement properties of Au nanostars, thus their strong SERS activity remained after tin oxide coating.     

Loss rate-based burst assembly to resolve contention in optical burst switching networks

Two loss rate-based optical burst assembly techniques addressing contention resolution are studied. These techniques stem from the burst assembly schemes using adaptive thresholds, which have been introduced earlier by the authors. The loss rates on the links/paths leading to the destination nodes are used to estimate congestion levels. Three alternative time and size threshold value pairs are employed based on the congestion level observed. Here, the aim is to generate short bursts under heavy traffic and long bursts under light traffic conditions in order to enhance performance. The results that are obtained in terms of byte loss rate and delay are compared with those of the hybrid burst assembly. It is observed that the adaptive techniques significantly enhance the byte loss rate as traffic gets heavier while keeping end-to-end delay in a feasible range.     

Oil migration in chocolate and almond product confectionery systems

Oil migration from high oil content almond confections into adjacent chocolate causes changes in product quality. The objective of this study was to quantify the oil migration from almond products to dark chocolate. Magnetic resonance imaging (MRI) was used to monitor spatial and temporal changes of liquid lipid content. A multislice spin echo pulse (MSSE) sequence was used to acquire images with a 7.8-ms echo time and a 1000-ms repetition time using a 1.03T Aspect AI MRI spectrometer. Samples were prepared as a 2-layer model system of chocolate and almond confection. Six different almond products and 1 type of dark chocolate were used. Samples were stored at 20, 25, and 30°C for a time frame of several months. Rate and extent of migration were quantified by a kinetic expression based on the linear dependence of oil uptake by chocolate and the square root of the time. Samples showed distinctly different rate and extent of oil migration, as evidenced by quantitative differences in the kinetic rate constants and equilibrium uptake for the different sample types. This work will be helpful to design formulations for almond and almond-based products in confections. PRACTICAL APPLICATION: This work will be helpful to design formulations for almond use in confections.     

Influence of exopolysaccharide‐producing cultures on the volatile profile and sensory quality of low‐fat Tulum cheese during ripening

The objective of this investigation was to compare the composition and changes in the concentration of volatiles in low‐fat and full‐fat Tulum cheeses during ripening. Tulum cheese was manufactured from low‐ or full‐fat milk using exopolysaccharide (EPS)‐producing or non‐EPS‐producing starter cultures. A total of 82 volatile compounds were identified belonging to the following chemical groups: acids (seven), esters (21), ketones (14), aldehydes (six), alcohols (14) and miscellaneous compounds (20). The relative amounts of acids, alcohols and aldehydes increased in the cheeses made with EPS‐producing cultures during 90 days of ripening. Differences were found in the volatile profile of full‐fat Tulum cheese compared with the low‐fat variant, especially after 90 days of ripening. Exopolysaccharide‐producing cultures changed the volatile profile, and the EPS‐producing cultures including Streptococcus thermophilus + Lactobacillus delbrueckii subsp. bulgaricus + Lactobacillus helveticus (LF‐EPS2) produced cheese with higher levels of methyl ketones and aldehydes than the non‐EPS cultures. In the sensory analysis, full‐fat Tulum cheeses and the cheese produced with the EPS‐producing culture containing Lb. helveticus (LF‐EPS2) were preferred by the expert panel. It was concluded that the use of EPS‐producing starter cultures in the manufacture of low‐fat Tulum cheese had the potential to improve the flavour.