Performance evaluation of polymer/clay nanocomposite thermal protection systems based on polyethylene glycol phase change material

Phase change materials (PCMs) are substances with a high heat of fusion which, through melting and solidifying at specified temperatures, are capable of storing or releasing a large amount of thermal energy. This phenomenon can be utilized in designing the heat protective materials as well as in the thermal energy storage systems. In this work, effects of polyethylene glycol (PEG) as PCM and montmorillonite nanoclay, as a thermal property modifier in epoxy resin on the thermal protection performance of nanocomposites were studied. A special performance evaluation test was designed to study the top surface temperature behavior of prepared samples under back surface heating. Results indicated that increasing PCM content improved thermal protection performance, but lower thermal diffusivity was found for the sample containing 60 wt% of PEG, with a 31 % decrease in top surface temperature. These results show that increasing of top surface temperature of samples containing PCM was very slow when compared with the neat epoxy sample. A top surface temperature behavior of these samples shows a plateau in melting region of PCM which makes a delay time in temperature increment compared with that of the neat epoxy sample. Moreover, heat protection performances of low filled nanocomposite blends, i.e., nanocomposite blends with 5 and 7 wt% of clay in PEG have been improved about 10 % in comparison with EP/PEG60 blend.     

Voltammetric determination of norepinephrine in the presence of acetaminophen using a novel ionic liquid/multiwall carbon nanotubes paste electrode

A novel multiwall carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was fabricated and used to investigate the electrochemical behavior of norepinephrine (NP). MWCNTs/CILE was prepared by mixing hydrophilic ionic liquid, 1-methyl-3-butylimidazolium bromide (MBIDZBr), with graphite powder, MWCNTs, and liquid paraffin. The fabricated MWCNTs/CILE showed great electrocatalytic ability to the oxidation of NE. The electron transfer coefficient, diffusion coefficient, and charge transfer resistant (R_ct) of NE at the modified electrode were calculated. Differential pulse voltammetry of NE at the modified electrode exhibited two linear dynamic ranges with slopes of 0.0841 and 0.0231 μA/μM in the concentration ranges of 0.3 to 30.0 μM and 30.0 to 450.0 μM, respectively. The detection limit (3σ) of 0.09 μM NP was achieved. This modified electrode exhibited a good ability for well separated oxidation peaks of NE and acetaminophen (AC) in a buffer solution, pH 7.0. The proposed sensor was successfully applied for the determination of NE in human urine, pharmaceutical, and serum samples.     

Enhancing the durability of multi-walled carbon nanotube supported by Pt and Pt–Pd nanoparticles in gas diffusion electrodes

This work tries to improve the durability of electrocatalysts of gas diffusion electrodes (GDEs) by using multi-walled carbon nanotube supported Pt–Pd bimetallic (Pt–Pd/MWCNT). The durability investigation of multi-walled carbon nanotube supported metals was evaluated by a repetitive potential cycling (RPC) corrosion test and by extended constant potential (ECP) experiments. Potential cycling tests were performed from −0.3 to 1.2 V at 50 mV s⁻¹ in 1 mol L⁻¹ H₂SO₄. Extended constant potential (ECP) durability test were also carried out on the GDEs by 30 h of constant potential operation at 0.8 V vs. Ag/AgCl. The smaller performance loss was observed on the GDE using Pt–Pd/MWCNT as electrocatalyst compared with GDE using Pt/MWCNT during both durability tests. ICP analysis also suggests that the dissolution of Pt nanoparticles from the carbon nanotube surface is hindered when Pd is present.     

Broadband microwave absorber based on patterned surface structure

Journal of Materials Science: Materials in Electronics - The limitations of traditional flat microwave absorbers in terms of material parameters make it challenging to improve the working...     

Evaluating knowledge management failure factors using intuitionistic fuzzy FMEA approach

The twenty-first century organizations are characterized by an emphasis on knowledge and information. Today’s organizations also require the acquisition, management, and exploitation of knowledge and information in order to improve their own performance. In the current economy, the foundations of organizational competitiveness have turned former tangible and intangible resources into knowledge and the focus of information systems has also changed from information management to knowledge management. Besides, the most important step in the implementation of knowledge management is to examine the significant factors in this regard and to identify the causes of failure. Therefore, the present study evaluated knowledge management failure factors in an intuitionistic fuzzy environment as a case study in Khuzestan Oil and Gas Company. For this purpose, a series of failure factors affecting knowledge management in organizations were identified based on a review of the related literature and similar studies. Then, 16 failure factors in the implementation of knowledge management in the given organization were determined on the basis of interviews with company experts. According to the specified factors as well as the integration of multiple criteria decision-making techniques in an intuitionistic fuzzy environment, knowledge management failure factors in Khuzestan Oil and Gas Company were investigated. The results indicated that lack of management commitment and leadership was the most important factor affecting the failure of knowledge management in the given company.     

Solubility and structure of milk powders manufactured with the addition of disodium phosphate and tetrasodium pyrophosphate mixtures

This study aimed to investigate the effect of adding binary mixtures of disodium phosphate and tetrasodium pyrophosphate during milk powder production. Overall, the addition of disodium phosphate–tetrasodium pyrophosphate caused an increase in pH and a decrease in the acidity and turbidity of reconstituted milk samples. The decrease in turbidity was attributed to either dispersion or swelling of the casein micelles. The addition of mixtures containing the lowest amounts of tetrasodium pyrophosphate considerably reduced the insolubility index, whereas mixtures containing higher levels of tetrasodium pyrophosphate exerted a detrimental effect on solubility. Interestingly, microscopic observations showed large agglomerated particles in mixtures with the highest level of tetrasodium pyrophosphate. We hypothesized that the formation of casein calcium–pyrophosphate complexes led to the higher insolubility index in this mixture.     

Content based similarity of geographic classes organized as partition hierarchies

In this paper we propose a method to measure the semantic similarity of geographic classes organized as partition hierarchies within Naive Geography. The contribution of this work consists in extending and integrating the information content approach, and the method for comparing concept attributes in the ontology management system SymOntos developed at IASI. As a result, this proposal allows us to address both the concept similarity within the partition hierarchy, and the attribute similarity of geographic classes and, therefore, to reduce the gap among the different similarity approaches defined in the literature.

Influence of Nitrogen on Hydrogenated Amorphous Carbon Thin Films Deposited by Plasma Focus Device

To carry out our research, a plasma focus device is used to deposit thin films of nitrogen doped hydrogenated amorphous carbon (a-C:H:N) onto the stainless steel-AISI-304 substrates at room temperature. Thin films are deposited with the same numbers of focus shots, at the same distance from the anode tip and with different partial pressures of nitrogen in the mixtures of acetylene/nitrogen as working gas. The nitrogen contents of deposited films are studied using nuclear reaction analysis (NRA) techniques. The results prove that nitrogen contents of the samples do not increase significantly by increasing partial pressure of nitrogen of the working gas for both sets of the samples. Moreover, NRA results exhibit the limitation of nitrogen incorporated into the samples, when this experimental setup is used. G-peak position and peak intensity ratio of the D-band to G-band (I_D/I_G) are used to investigate the diamond characters. Also, they show that sp² clustering is highly dependent on the nitrogen atomic contents and angular position of the samples. Scanning electron microscopy (SEM) shows the granular surface morphology of the films. Furthermore, it shows that angular position of the samples with respect to the anode axis plays an important role in the grain size of the surface of the samples. The thickness of the films decreases significantly by increasing angular position of the samples, while it decreases slightly by increasing partial pressure of nitrogen of the working gas. The Vickers surface hardness of the thin films exhibits significant dependency on the sp² clustering.     

Extraction of amino acids from protein hydrolysates by electrodialysis

Protein hydrolysates were obtained by acid hydrolysis from animal or human residues, such as poultry feathers, ox blood and human hair. After neutralization and discolouration with active charcoal, the hydrolysates were treated by successive electrodialysis (ED) in order to extract amino acids into several fractions. The current density and pH were optimized for each ED operation performed with preindustrial pilot scale equipment. The first step was the demineralization of amino acid mixtures using an ED stack with two compartments. The salt removal was achieved with extraction degrees higher than 90% and current efficiencies of about 80%. In the most favourable case, the amino acid losses did not exceed 10%. The second step was the extraction of the charged amino acids using an ED stack with four compartments. Three fractions were obtained, corresponding to the acidic, basic and neutral amino acids. The extraction degrees varied from 80% to 100%. In the third step, the fractionation of basic amino acids on the one hand, and neutral amino acids on the other hand, was carried out with enrichment degrees varying from 50% to 80%. © 1998 SCI