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21.
A change in finite element size causes spurious reflection of elastic waves passing through a finite element grid when the wavelength is less than about 10-times the largest element in the grid. Extending the previously published study in which the phenomenon was analyzed for the case of constant strain finite elements, the higher-order elements with linear strain distribution are studied herein. Similarly to the previous study, it is found that the consistent mass matrix gives less spurious wave reflection than the lumped mass matrix; however the advantage is smaller for the higher-order elements. For the lumped mass matrix, there is little difference in spurious wave reflection between the constant strain and linear strain elements. The phenomenon of spurious wave reflection is less pronounced when the higher-order elements are used in conjunction with the consistent mass matrix. These results are obtained from exact analytical solutions in complex variables for a planar wave with a planar wave front propagating along grid lines through an infinite grid which is uniform in each half plane. 相似文献
22.
Mohamed Nadjib Boukhatem Abdelkrim Kameli Mohamed Amine Ferhat Fairouz Saidi Khadidja Tayebi 《Journal für Verbraucherschutz und Lebensmittelsicherheit》2014,9(1):13-21
Several essential oils of medicinal plants possess proven antimicrobial activity and are suitable for applications on the food industry. The oil from Cymbopogon citratus (lemongrass) has been reported to have a wide range of biological activities. However, there are few controlled studies confirming its antimicrobial activity. The aim of our study was to assess the antimicrobial potential of lemongrass oil against a wide spectrum of food spoilage and pathogenic bacteria and yeast in liquid and vapour phase. The chemical composition of the oil was analyzed by gas chromatography; 14 components were identified and geranial (28.93 %), neral (24.30 %) and myrcene (23.92 %) were the most abundant constituents. Lemongrass oil showed potent antimicrobial activity against Gram positive bacteria and exhibited the strongest antifungal effect against Candida albicans and C. parapsilosis. Minimum inhibitory concentration varied from 0.019 to 1.25 mg mL?1 for Gram positive bacteria and yeasts, indicating Staphylococcus aureus, S. epidermidis and C. albicans as the most susceptible strains. Moreover, the diameter of inhibition zone (DIZ) increased with increasing essential oil (EO) volume. Considerably superior antimicrobial activity was observed in the vapour phase. The DIZ resulting from the exposure to EO vapour was significantly larger than that from the same volume in the liquid phase. The DIZ varied from 22 to 90 mm for Candida strains. There is growing evidence that EO in vapour phase are effective antimicrobial systems and that they do have advantages over the use of oil in liquid phase. Our results imply that lemongrass oil could be useful for the development of novel types of natural preservatives for food control. 相似文献
23.
In this study, the thermal comfort properties of single jersey fabrics produced by conventional and hollow cotton yarns with different hollowness ratio have been investigated and compared. For this purpose, thermal conductivity, thermal resistance, thermal absorptivity, air permeability and water vapour permeability of core spun, hollow and conventional yarn fabrics were measured and evaluated statistically. It was observed that thermal comfort properties of single jersey fabrics were affected by the yarn structure and the fibre distribution within the yarn. The results showed that hollow yarn fabrics had better thermal comfort properties than that of conventional yarn fabrics. In hollow yarns, as the hollowness ratio increases, air permeability and thermal conductivity of single jersey fabrics decrease but thermal resistance, thermal absorptivity and water vapour permeability increase. Statistical analysis also indicated that the differences between properties of hollow yarn fabrics and conventional yarn fabrics were significant. Furthermore, the yarn hollowness ratio significantly affects thermal comfort properties of single jersey fabrics. 相似文献
24.
This study presents a method validation procedure for the determination of aflatoxin B1, B2, G1, and G2 in hazelnut, hazelnut paste, walnut, peanut, pistachio, corn, and wheat. The method consisting of clean-up with immunoaffinity column, high performance liquid chromatography with postcolumn derivatization and fluorescence detection was validated in accordance with Commission Regulation 2004/882/EC. The selectivity, linearity, decision limit, detection capability, detection and quantification limits, precision, recovery, ruggedness, and measurement uncertainty of the method were determined. The limit of detection and limit of quantification values (μg/kg) were: aflatoxin B1, 0.02, 0.07; aflatoxin B2, 0.01, 0.02; aflatoxin G1, 0.02, 0.07; and aflatoxin G2, 0.01, 0.03. The relative standard deviation values for the repeatability and within-laboratory reproducibility were below 4 and 5 %, respectively. The recovery values of the spiked samples ranged from 80 to 105 %. These results complied with minimum performance criteria established by regulation 2006/401/EC. Therefore, the procedure can be implemented for the routine analysis of aflatoxins in the studied matrices. 相似文献
25.
Meliha Oktav Bulut Cihan Devirenoğlu Lutfi Oksuz Ferhat Bozdogan Erdogan Teke 《纺织学会志》2013,104(8):828-841
In this study, corona plasma discharge was applied to desize polyvinyl alcohol (PVA) and starch on cotton fabrics. Plasma treated and non-treated samples were processed in various steps in a textile firm. The samples were tested to evaluate their weight loss, size dissolution, capillarity, dyeability, pilling resistance and strength values. The surface morphology and the chemical structures were examined by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy analyses. The experimental results showed that the plasma has positive effects on size removal, hydrophility and the pilling values of the PVA and also starch sized fabrics. 相似文献
26.
Chemical reactivity of mineral aggregates in aqueous solution: relationship with bitumen emulsion breaking 总被引:1,自引:1,他引:0
Layella Ziyani Vincent Gaudefroy Valéry Ferber Dimitri Deneele Ferhat Hammoum 《Journal of Materials Science》2014,49(6):2465-2476
This paper reports a study on chemical reactivity of gneiss, diorite and limestone aggregates in aqueous solution. The originality of this study is that it extended to very short times (less than 1440 min). Rise in pH tests was implemented and dissolution kinetics was analysed. The results showed that calcium was the major element released by the aggregates. It has also been found that dissolution had an influence on the final morphology of aggregates. Polyamine emulsifier adsorption onto aggregates has been assessed using electrophoresis. Finally, the rise in pH and electrophoretic tests were compared to the breaking test traditionally performed to characterise bitumen emulsions. It was found that breaking values were controlled by both the surface area and the surface charge of the particles. Results may be correlated to polyamine adsorption on aggregates. Adsorption seemed to be efficient for gneiss and diorite: at pH 2, their charge turned from slightly negative to highly positive. At this pH value, limestone particles were dissolved and polyamine adsorption must be less efficient than with gneiss and diorite, for which the emulsion breaking was facilitated by the high attraction of particles for the emulsifier, due to their negative surface charge. 相似文献
27.
Carlos Colman-Meixner Ferhat Dikbiyik M. Farhan Habib Massimo Tornatore Chen-Nee Chuah Biswanath Mukherjee 《Photonic Network Communications》2014,27(3):141-153
Cloud-computing services are provided to consumers through a network of servers and network equipment. Cloud-network (CN) providers virtualize resources [e.g., virtual machine (VM) and virtual network (VN)] for efficient and secure resource allocation. Disasters are one of the worst threats for CNs as they can cause massive disruptions and CN disconnection. A disaster may also induce post-disaster correlated, cascading failures which can disconnect more CNs. Survivable virtual-network embedding (SVNE) approaches have been studied to protect VNs against single physical-link/-node and dual physical-link failures in communication infrastructure, but massive disruptions due to a disaster and their consequences can make SVNE approaches insufficient to guarantee cloud-computing survivability. In this work, we study the problem of survivable CN mapping from disaster. We consider risk assessment, VM backup location, and post-disaster survivability to reduce the risk of failure and probability of CN disconnection and the penalty paid by operators due to loss of capacity. We formulate the proposed approach as an integer linear program and study two scenarios: a natural disaster, e.g., earthquake and a human-made disaster, e.g., weapons-of-mass-destruction attack. Our illustrative examples show that our approach reduces the risk of CN disconnection and penalty up to 90 % compared with a baseline CN mapping approach and increases the CN survivability up to 100 % in both scenarios. 相似文献
28.
Ferhat Djerboua Zohra Djetoui 《材料科学与工程:中英文B版...》2013,(8):498-503
Nowadays many studies have been focusing on the development of biomaterials obtained from renewable resources to replace fossil based plastics. The famous example is starch which is produced by a wide variety of plants as energy reserve and is available in abundance at a very competitive price. It can easily be transformed into thermoplastic starch (TPS) by addition of a plasticizer. However, TPS suffers from several limitations, such as poor mechanical properties and water sensitivity which did not permit its use in large practical applications. In this study, different formulations, containing commercial corn starch and plasticizers were prepared by the film casting method, after gelatinization of starch in hot aqueous suspensions. To obtain flexible films, two plasticizers were used: glycerol and dioctyl phthalate (DOP). The fact that the DOP displayed an exceptionally poor water affinity, three co-solvents, methanol, ethanol and acetone were added in the aim to improve its solubility. The obtained materials were tested considering the water resistance measured at 25 and at 50 ℃, mechanical properties in tension and the differential scanning thermal analysis (DSC). From the obtained results, it seems that the solvent system as well as the plasticizers used affects considerably the properties of the resulting materials. 相似文献
29.
The aim of this study was to improve thermal conductivity, thermal stability, and mechanical properties of bisphenol A dicyanate ester (BADCy) by adding bisphenol A dicyanate ester containing fluorine (F‐BADCy) and nano diamond. The cyanate esters containing fluorine/nano diamond composites having various ratios of BADCy, F‐BADCy, and nano diamond were prepared. Thermal stability and thermal conductivity of the samples were evaluated by thermogravimetric analysis, differential scanning calorimetry and laser flash method, respectively. The samples were characterized with the following analysis; gel content, water absorption capacity, and stress‐strain test. Hydrophobicity of the samples was determined by the contact angle measurements. Moreover, the surface morphology of the samples was investigated by a scanning electron microscopy (SEM). The obtained results prove that the cyanate ester containing fluorine/nano diamond composites have good thermal and mechanical properties and they can be used in many applications such as electronic devices, materials engineering, and other emergent. POLYM. COMPOS., 34:1977–1985, 2013. © 2013 Society of Plastics Engineers 相似文献
30.
Awadesh Kumar Mallik Nurcan Calis Acikbas Ferhat Kara Hasan Mandal Debabrata Basu 《Ceramics International》2012,38(7):5757-5767
Two different varieties of Si3N4 powders were used to prepare SiAlON ceramics. 100% β-Si3N4 was used from refractory grade powders (B1) and another purer 98% α-Si3N4 (50A) powder was used to prepare the SiAlON samples. Since SiC + SiAlON composites reportedly perform better, batches were prepared with 15% SiC addition to the refractory powders (B1) and 17.5% SiC was added to the other SiAlON composition (50A). The samples were gas pressure sintered at 1840 °C and at 22 bar with 1 h dwelling time. Thereby, we could achieve 97–98% theoretical density. The hardness was recorded 14–17 GPa while fracture toughness varied from 4.3 to 5 MPa m1/2. Fretting experiments showed initial running-in period of 300 cycles for all the tribo-couples. After which, the steady state coefficient of frictions (COF) were achieved. Steel ball of 10 mm diameter, fretting against 50A composition, showed 0.6 average steady state COF while the same composition while fretting against alumina ball of the same diameter, showed 0.57 average steady state COF. Results have been compared with SiAlON composition derived from refractory powder (B1) and found that the 50A composition performs better under identical test conditions. Moreover, cytocompatibility study also suggests that the investigated 50A composition can be used as substrate to support cell adhesion and proliferation of L929 mouse fibroblast cell lines whereas B1 composition derived from refractory powders are toxic in nature. 相似文献