Time filter

Source Type

Sajedi F.,Islamic Azad University at Ahvaz | Razak H.A.,University of Malaya | Mahmud H.B.,University of Malaya | Shafigh P.,Science and Research Branch
Construction and Building Materials | Year: 2012

In this investigation 12 mortar mixes including three groups were prepared using binder contents 380 and 500 kg/m 3. All the specimens were cured after casting and demoulding in curing regimes, i.e. at room temperature (ac) and in water (wc). The highest strength was obtained for cement-slag mortars 380-wc at later ages as 80 MPa. For all groups of mortars, there could rarely be strength loss at later ages. It was observed that in duration of 3-7 days, wc is the optimum for all groups of mortars with exception of cement mortar 500 and slag mortar 500. In duration of 28-90 days, wc is also the optimum for three groups of mortars with exception of cement mortar 500. It was revealed that an exponential relationship exists between the strengths obtained in air and water curing conditions for each group of mortar, i.e. with and without using ground granulated blast furnace slag. It was proved that higher strengths could be obtained using lower binders' contents for cement and cement-slag mortars provided the specimens were cured in water. This is a new finding having importance from economic and environmental viewpoints; meaning that for producing higher strengths it is not a necessity to use more binders. It was found that increase in level of cement and slag makes the mortars more sensitive to air curing conditions. © 2012 Elsevier Ltd. All rights reserved. Source

Khaki S.,Science and Research Branch
International Journal of Applied Linguistics and English Literature | Year: 2013

WTC is very important for English learners. Without WTC it is impossible to use the target language. On the other hand, developing learner autonomy as the independence in one’s own learning is considered a crucial goal of education. More important than that learner autonomy in WTC is a necessity that has to be considered in language education. In this study, the researcher investigated whether there is any statistically significant relationship between learner autonomy and WTC in Iranian EFL learners. To this end, 77 English learners were homogenized out of 100 advanced learners. A learner autonomy questionnaire and a WTC scale, for measuring trait-like WTC, was given to them; and they were observed, for measuring situational WTC, for 6 sessions. The quantitative data gathered through these instruments were analyzed to determine the degree of correlation between these two constructs. The results demonstrated a significant and strong relationship between learner autonomy and trait-like WTC in Iranian EFL learners and a significant but weak correlation between learner autonomy and situational WTC in Iranian EFL learners. So it can be concluded that a significant relationship between learner autonomy and WTC can be seen in Iranian EFL learners. The regression analysis provided further support for this result. © Australian International Academic Centre, Australia. Source

Sepehrian H.,Nuclear Science and Technology Research Institute, Iran | Ahmadi S.J.,Nuclear Science and Technology Research Institute, Iran | Waqif-Husain S.,Science and Research Branch | Faghihian H.,University of Isfahan | Alighanbari H.,Shahid Beheshti University
Journal of Hazardous Materials | Year: 2010

Mesoporous aluminosilicates, have been prepared with various mole ratios of Si/Al and Cethyltrimethylammonium bromide (CTAB). They have been characterized by XRD, nitrogen adsorption/desorption measurements, FT-IR and thermogravimetry. Adsorption behavior of heavy metal ions on this adsorbent have been studied and discussed. The results show that incorporation of aluminum ions in the framework of the mesoporous MCM-41 has transformed it into an effective cation exchanger. The Kd values of several metal ions have been increased. Separation of Sr(II)-Ce(III), Sr(II)-U(VI) and Cd(II)-Ce(III) has been developed on columns of this novel mesoporous cation exchanger. © 2009 Elsevier B.V. All rights reserved. Source

Naimi B.,University of Twente | Naimi B.,Science and Research Branch | Skidmore A.K.,University of Twente | Groen T.A.,University of Twente | Hamm N.A.S.,University of Twente
Journal of Biogeography | Year: 2011

Aim To investigate the impact of positional uncertainty in species occurrences on the predictions of seven commonly used species distribution models (SDMs), and explore its interaction with spatial autocorrelation in predictors. Methods A series of artificial datasets covering 155 scenarios including different combinations of five positional uncertainty scenarios and 31 spatial autocorrelation scenarios were simulated. The level of positional uncertainty was defined by the standard deviation of a normally distributed zero-mean random variable. Each dataset included two environmental gradients (predictor variables) and one set of species occurrence sample points (response variable). Seven commonly used models were selected to develop SDMs: generalized linear models, generalized additive models, boosted regression trees, multivariate adaptive regression spline, random forests, genetic algorithm for rule-set production and maximum entropy. A probabilistic approach was employed to model and simulate five levels of error in the species locations. To analyse the propagation of positional uncertainty, Monte Carlo simulation was applied to each scenario for each SDM. The models were evaluated for performance using simulated independent test data with Cohen's Kappa and the area under the receiver operating characteristic curve. Results Positional uncertainty in species location led to a reduction in prediction accuracy for all SDMs, although the magnitude of the reduction varied between SDMs. In all cases the magnitude of this impact varied according to the degree of spatial autocorrelation in predictors and the levels of positional uncertainty. It was shown that when the range of spatial autocorrelation in the predictors was less than or equal to three times the standard deviation of the positional error, the models were less affected by error and, consequently, had smaller decreases in prediction accuracy. When the range of spatial autocorrelation in predictors was larger than three times the standard deviation of positional error, the prediction accuracy was low for all scenarios. Main conclusions The potential impact of positional uncertainty in species occurrences on the predictions of SDMs can be understood by comparing it with the spatial autocorrelation range in predictor variables. © 2011 Blackwell Publishing Ltd. Source

Yadegari H.,K. N. Toosi University of Technology | Jabbari A.,K. N. Toosi University of Technology | Heli H.,Science and Research Branch | Heli H.,Islamic Azad University at Science and Research of Fars
Journal of Solid State Electrochemistry | Year: 2012

Nanoparticles of lithiumcobalt oxide (LiCoO 2) and nanosheets of lithium vanadium oxide (LiV 3O 8) were synthesized by a citrate sol-gel combustion route. The physical characterizations of the electrodic materials were carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and also X-ray diffraction (XRD) measurements. Near spherical nanoparticles of 100 nm and compact nanosheets with a few nanometers thick were observed by SEM and TEM for LiCoO 2 and LiV 3O 8, respectively. XRD data indicated that the asprepared active materials presented pure phase of rhombohedral LiCoO 2 with R-3m symmetry and monoclinic LiV 3O 8 with p21/m symmetry. The kinetics of electrochemical intercalation of lithium ion into the nanoparticles of LiCoO 2 and nanosheets of LiV 3O 8 from 1.0 mol l-1 LiNO3 aqueous solution were investigated by cyclic voltammetry and chronoamperometry. An aqueous rechargeable lithium-ion battery consisting of LiCoO 2 nanoparticles as positive and LiV 3O 8 nanosheets as negative electrode was assembled. This battery represented a discharge voltage of about 1 V with good cycling performance. © Springer-Verlag 2011. Source

Discover hidden collaborations