Impedance investigation of thermally formed oxide films on AISI 304L stainless steel

Thin oxide layers on 304L stainless steel were grown by thermal oxidation at 300 °C at different durations ranging from 2 to 4 h. The structural characterization of the oxide films was carried out by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Electrochemical impedance spectroscopy was used to investigate the effects of exposure time and applied potential on the electronic properties of these films. Oxide films are described by a multilayer structure, with n-type iron oxide and oxyhydroxide in the outer layers and p-type chromium oxide in the inner layer. Doping densities evaluated from Mott-Schottky plots increased with the oxidation duration, with characteristics of highly disordered semiconductor.     

Optimization of Microchannel Heat Sinks Using Genetic Algorithm

In this study, a genetic algorithm is employed to minimize the entropy generation rate in microchannel heat sinks. The entropy generation rate allows the combined effects of thermal performance and pressure drop to be assessed simultaneously as the heat sink interacts with the surrounding flow field. Previously developed models for the heat transfer, pressure drop and entropy generation rate are used in the optimization procedure. The results of optimization are compared with existing results obtained by the Newton–Raphson method. It is observed that the GA gives better overall performance of the microchannel heat sinks.     

Phase formation of REBa2Cu3O7−δ (RE: Y0.5Gd0.5, Y0.5Nd0.5, Nd0.5Gd0.5) superconductors from nanopowders synthesised via co-precipitation

Phase formation of REBa₂Cu₃O_7−δ (RE: Y_0.5Gd_0.5, Y_0.5Nd_0.5, Nd_0.5Gd_0.5) superconductors synthesised via co-precipitation (COP) method were investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis. All samples showed identical thermal decomposition behaviour from the thermogram in which 5 major weight losses were observed. However, XRD of the samples at different heat treatment temperatures showed different diffraction patterns indicating different thermolytic processes. Meanwhile, transmission electron microscopy and surface area analysis revealed that the powders obtained from COP have particle sizes ranging from 7 to 12 nm with relatively large surface area. Molar ratios of prepared samples obtained were near to the theoretical values as confirmed by elemental analyses using X-ray fluorescence (XRF). The T_C(R=0) for sintered YGd, YNd and NdGd were 87 K, 86 K and 90 K, respectively. Surface morphological study via scanning electron microscope showed the structures of samples were dense and non porous.     

Effect of the length and the volume fraction of wavy steel fibers on the behavior of self-compacting concrete

Self-compacting concrete (SCC) is a highly workable concrete that fills formwork under its own weight (without any vibration or impact). It also passes easily through small spaces between reinforcement bars. The inclusion of fibers in such concrete limits the concrete shrinkage cracks at early age and enhances some of its properties. However, fibers may affect the flow characteristics of SCC. In this paper, three wavy steel fibers (SF) of different lengths, 35, 40, and 50 ± 2 mm with six different volume fractions (V_f) of 0.3, 0.5, 0.8, 1, 1.2, and 1.4% were used in SCC. The experimental results showed that the addition of SF with higher V_f content and longer length decreases the workability of SCC, reduces its passing ability and increases the possibility of blockage. Mechanical performances of concrete in terms of flexural strength and elasticity modulus were improved, where the slightly compressive strength decreased with an increase in V_f content of SF.     

Wood fuel trade in European Union

Wood fuels are the most important alternatives of fossil fuel which is one of the reasons of the climate changes in the world and of global warming. Wood fuels, which have an important role in the cause of both providing energy requirement of production units and heating for household and healing energy deficit, disperse very less CO₂ than fossil fuels to atmosphere. Bio-fuels are used to provide energy requirement among EU countries like using in lots of developed countries. Resources having by lots developed countries and EU countries are not at enough level for bio-fuels. For this reason, trade of bio-fuels has been become in an important situation in recent years. In this study, import and export levels of bio-fuels of EU countries and Turkey, which is a candidate for union, were investigated between 2003 and 2006. The date is obtained from European Forest Institute (EFI) forest products trade flow database. As a result of the study, while rises were determined in years, it is determined that the most important exporters are Germany, Italy, Latvia and Poland and the most important importers are Germany, Italy, Belgium and UK. It is seen that Turkey has a low trade level in selected product groups.     

Vaccination of patas monkeys experimentally infected with Schistosoma haematobium using a recombinant glutathione S-transferase cloned from S. mansoni

The capacity of a recombinant glutathione S-transferase from Schistosoma mansoni (rSm28GST) to vaccinate primates (Erythrocebus patas) against a heterologous infection with Schistosoma haematobium has been tested. Two injections of the purified molecule with Muramyl-Di-Peptide (MDP) as adjuvant resulted in a high level antibody response in the five immunized animals and in a significant reduction in worm fecundity compared to the controls which received adjuvant alone. Mean levels of daily egg excretion in urine an faeces were reduced by respectively 55% and 74% although perfusion revealed that worm burdens were similar in both groups. The protective effect was long lasting since it was maintained up to the end of the experiment, 42 weeks after infection. Hatching rates and the numbers of intra-uterine eggs were also significantly affected by the vaccination. Tissue eggs were also drastically diminished in the urogenital system (-80%) but the reduction was not statistically significant. One animal was not protected by the immunization. There was a good correlation between parasitological data and the intensity of bladder lesions assessed by microscopic examination. Polypoid formations together with an intense exudation of the lamina propria were frequently seen in the controls but rarely in the vaccinated group where formation of scar tissue was predominant. These results underline the vaccine potential of the recombinant Sm28GST as a possible valuable prophylactic tool for the control of egg-induced pathology and transmission of African schistosomes.     

Hydroxymethylation and polycondensation reactions in urea–formaldehyde resin synthesis

Formaldehyde–urea (F/U) reaction products with molar ratios of 1.8, 2.1, and 2.4 were synthesized at pH 8.3, and the last one also at pH 4.5 using 45% formaldehyde aqueous solution. For obtaining the resin, the synthesis of F/U 2.1 was continued by acid‐catalyzed condensation at pH 4.5 and posttreatment with second part of U (F/U 1.05/1) at 70°C and pH 8.3. The products were analyzed using ¹³C‐NMR spectrometry. Higher excess of F increases the dihydroxymethyl content on account of smaller dimethylene ether content. Certain ¹³C chemical shifts in carbonyl and methylene region of spectra were assigned to trishydroxymethylurea, being the main trisubstituted urea compound in hydroxymethylated product. Acid catalyst promotes the formation of methylene groups by polycondensation of hydroxymethyl groups, against the background of similar content of dimethylene ethers in both catalytic conditions. The ratio of linear/branched chains is emphasized in characterizing the resin structure. Higher hydroxymethyl content in acid‐catalyzed polycondensation is an advantage of three‐step synthesis technology. The amount of binding methylene and dimethylene ether groups linked only to secondary amino groups can be increased by transhydroxymethylation with subsequent polycondensation in posttreatment with U in suitable reaction conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1673–1680, 2006     

Sustainable GQDs for potential application in engineering using corn powder as green precursor

Abstract

An alternative way to produce Graphene Quantum Dots (GQDs) economically is proposed in this study where corn powder was used as a green precursor to fabricate GQDs in a hassle less one-step route. These GQDs showed a stable, size-dependent in aqueous solution. The size of GQDs obtained from this work is approximately measure from 0.21 to 5.20?nm. The XRD patterns showed a broad peak at 22?Å. Furthermore, the UV-vis absorption spectrum has a broad peak around the range of 250–350?nm which is ascribed to the typical absorption of n-π* transition of the carbonyl groups. The said sample also exhibited bright green photoluminescence under an UV light. The Raman spectra displayed a D band around 1375?cm^?1 and G band around 1578?cm^?1. The performed analysis confirms that the GQDs by this method has a similar result compared to the other methods. This suggests that corn powder as a precursor can be used to fabricate GQDs in a simplistic and environment-friendly way for potential application in sensors, very large scale integration and energy generation technology.     

Effect of metakaolin and foundry sand on the near surface characteristics of concrete

This paper deals with the effect of foundry sand (FS) and metakaolin (MK) on the near surface characteristics of concrete. A control concrete having cement content 450 kg/m³ and w/c of 0.45 was designed. Cement was replaced with three percentages (5%, 10%, and 15%) of metakaolin weight, and fine aggregates were replaced with 20% foundry sand. Tests were conducted for initial surface absorption, sorptivity, water absorption and compressive strength at the ages of 35, 56, and 84 days.Test results indicated that with the increase in MK content from 5% to 15%, there was a decrease in the initial surface absorption, decrease in the sorptivity till 10% metakaolin replacement. But at 15% MK replacement an increase in sorptivity was observed. All mixtures showed low water absorption characteristic i.e. less than 10%. Compressive strength shared an inverse relation with sorptivity. Higher MK replacements of 15% are not helpful in improving inner core durability, even though it helps in improving surface durability characteristics. Inclusion of foundry sand resulted in reduction in compressive strength. This aspect cements the findings that addition of FS causes permeability of concrete to increase causing in an increase in sorptivity and water absorption of concrete.