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11.
Properties of pumice aggregate concretes at elevated temperatures and comparison with ANN models
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The mechanical properties and thermal conductivity of concretes including pumice aggregate (PA) exposed to elevated temperature were analyzed by thermal conductivity, compressive strength, flexure strength, dynamic elasticity modulus (DEM) and dry unit weight tests. PA concrete specimens were cast by replacing a varying part of the normal aggregate (0–2 mm) with the PA. All concrete samples were prepared and cured at 23 ± 10C lime saturated water for 28 days. Compressive strength of concretes including PA decreased that reductions were 14, 19, 25 and 34% for 25, 50, 75 and 100% PA, respectively. The maximum thermal conductivity of 1.9382 W/mK was observed with the control samples containing normal aggregate. The tests were carried out by subjecting the samples to a temperature of 0, 100, 200, 300, 400 500, 600 and 700 °C for 3 h, then cooling by air cooling or in water method. The results indicated that all concretes exposed to a temperature of 500 and 700 °C occurred a significant decrease in thermal conductivity, compressive strength, flexure strength and DEM. An artificial neural network (ANN) approach was used to model the thermal and mechanical properties of PA concretes. The predicted values of the ANN were in accordance with the experimental data. The results indicate that the model can predict the concrete properties after elevated temperatures with adequate accuracy. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
12.
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
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14.
Message Sequence Charts (MSC) is a graphical and textual specification language developed by ITU-T. It is widely used in telecommunication software engineering for specifying behavioral scenarios. Recently, the time concept has been introduced into MSC'2000. To support the specification and verification of real-time systems using timed MSC, we need to define its formal semantics. In this paper, we use timed lposet as a semantic model and give a formal semantics for timed MSC. We first define an event in a timed MSC as a timed lposet, then give a formal semantics for timed basic MSCs, timed MSCs with structures and high-level MSCs. In this paper, we also discuss some important issues related to timed MSC. 相似文献
15.
The shear stress–strain behaviour of two low-modulus structural adhesives has been measured using the butt-torsion test. The Nadai correction for non-linear shear behaviour is explained as it is necessary to understand how this correction can be applied to butt joints. The results for one adhesive were accurately used to predict the strength of a lap joint, and it was shown that the strength of such a joint can approach that of a conventional, modern, structural epoxy. Structural adhesives are usually reckoned to be those with a high strength (50 MPa and upwards) and (these days), a strain to failure of at least 10% in tension, and which usually have a tensile modulus of 2 GPa or so. However, adhesives which are significantly less stiff, less strong, but much more ductile are entering the ‘structural’ arena. In order to evaluate their effectiveness and use in design, it is necessary to be able to measure accurately their stress–strain behaviour. Two such materials are 3M 9245 Structural Bonding Tape (SBT) and 3M 7838 B/A. 相似文献
16.
We present a theoretical study mainly devoted to the investigation of the bowing parameter in the GaAs1–xBix alloy. Results reveal that the fundamental band gap for GaAs is close to 0.08 eV and it corresponds to −2.01 eV for GaBi. The addition of Bi to GaAs serves to make the lattice constant of the crystal larger than GaAs and distorts the valence band. This causes an intrinsic asymmetry between the carrier mobility. The band gap of GaAsBi alloy decreases with increasing Bi content. Moreover, the non-linear variation of the lattice parameter is clearly visible with upward bowing parameter, equal to −0.378 ± 0.16 Å. Compared with preceding works on the matter, the band gap versus composition is well fitted with a downward bowing parameter of 1.74 ± 0.51 eV. This shows that the direct band gap of this alloy covers a spectral region ranging from near infrared to infrared. 相似文献
17.
Ferhat Yücedag Cigdem Atalay‐Oral Sibel Erkal Ahmet Sirkecioglu Djursun Karasartova Fikret Sahin Serife Birgül Tantekin‐Ersolmaz Fatma Seniha Güner 《应用聚合物科学杂志》2010,115(3):1347-1357
As an alternative to petroleum‐based polyol, hydroxyl containing material was prepared from linseed oil for polyurethane synthesis. Hexamethylene di‐isocyanate (HMDI) and/or 4, 4′‐methylene diphenyl di‐isocyanate (MDI) were used as isocyanate source. The polymerization reaction was carried out without catalyst. Polymer films were prepared by casting‐evaporation technique. The MDI/HMDI‐based polyurethane and its films had higher Tg and better thermal property than that of the HMDI‐based one because of the existence of benzene ring in the polymer chain. Static water contact angle was determined to be 74° and 77.5° for HMDI and MDI/HMDI‐based films, respectively. Water adsorption was found to be around 2.6–3.6% for both films. In vitro degradation of polyurethanes in phosphate buffered saline at 37°C was investigated by gravimetric method. Fourier transform infrared spectroscopy and scanning electron microscopy were used for confirmation of degradation on the polymer surface. The degradation rate of the HMDI‐based polyurethane film was found higher than that of the MDI/HMDI‐based film. Both the direct contact method and the MMT test were applied for determination of cytotoxicity of polymer films, and the polyurethane films investigated here was not cytotoxic. Silver‐containing films were prepared using Biocera A® as filler and were screened for their antibacterial performance against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and/or Bacillus subtilis. The films prepared with and without Biocera A® exhibited antibacterial activity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
18.
A. Zaoui M. Certier M. Ferhat W. Sekkal O. Pags H. Aourag 《Computational Materials Science》2000,17(2-4):400-403
The charge density of Ge was studied at various k-points and for various bands, by the ab initio pseudopotential method, using additionally the interstitial sites. The lowest Xc conduction-band points were found to be unique in having a high charge density in the interstitial site. It has been therefore predicted and verified that the Xc points move up in energy relative to the Γc point when closed-shell atoms (like H) are substituted at the interstitial sites. The calculations also indicate the change of the band-gap for HGeH. 相似文献
19.
Abdullah Goktas Ferhat Aslan ?brahim Halil Mutlu 《Journal of Materials Science: Materials in Electronics》2012,23(2):605-611
The effect of annealing temperature on selected characteristics of polycrystalline La0.67Sr0.33MnO3 films, which have been produced on quartz substrates, was investigated. X-Ray powder diffraction patterns showed that the
phase formation started at 873 K and all the films had perovskite structure. By increasing the annealing temperature, the
lattice parameters were decreased. Scanning electron microscope indicated that the film thicknesses were approximately 3 μm
and the average grain size of the samples varied between 30–100, 50–110, 70–120, and 100–150 nm for films annealed at 873,
973, 1,073, and 1,173 K, respectively. All the films showed a paramagnetic–ferromagnetic (TC) and metal–insulator (TIM) phase transition. The TC indicated a small variation [from 131 K (S4) to 124 K (S1)] as a function of annealing temperature, whereas the TIM went down from 212 K (S4) to 110 K (S1), a strong decrease of 102 K. A colossal magneto resistance with magneto resistance
ratios of 130, 139, 156, and 163% were observed near TC and at 6 T magnetic field. 相似文献
20.
The compressive strength of normal strength concrete at elevated temperatures up to 700°C and the effect of cooling regimes were investigated and compared in this study. Thus, two different mixture groups with initial strengths of 20 and 35 MPa were produced by using river sand, normal aggregate and portland cement. Thirteen different temperature values were chosen from 50 to 700°C. The specimens were heated for 3 h at each temperature. After heating, concretes were cooled to room temperature either in water rapidly or in laboratory conditions gradually. The residual strengths were determined by an axial compressive strength test. Strength and unit weight losses were compared with the initial values. Throughout this study, ASTM and Turkish Standards were used. It was observed that concrete properties deteriorated with the heat; however, a small increase in strength was observed from 50 to 100°C. Strength loss was more significant on the specimens rapidly cooled in water. Both concrete mixtures lost a significant part of their initial strength when the temperature reached 700°C. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献