Evaluating and forecasting the initial and final setting times of self-compacting concretes containing mineral admixtures by neural network

An experimental study was conducted to investigate the effects of using binary, ternary, and quaternary cementitious blends of portland cement (PC), fly ash (FA), ground granulated blast furnace slag (GBS), silica fume (SF), and metakaolin (MK) on initial and final setting times of self-compacting concretes (SCCs). For this purpose, a total of 65 SCC mixtures were prepared at two different water binder ratios. Furthermore, based on the experimental results, neural network (NN) model-based explicit formulations were developed to predict the initial and final setting times of SCCs in terms of the amount of concrete constituents, namely mixing water, PC, FA, GBS, SF, MK, fine (fa) and coarse (ca) aggregates, and superplasticizer (SP). The test results have revealed that the mineral admixtures were very effective on the initial and final setting times of SCCs. Besides, it was found that the model developed by using NN seemed to have a high prediction capability of initial and final setting times of SCCs.     

Investigation of the mechanism of lubrication in starch–oil composite dry film lubricants

The boundary coefficient of friction (COF) of starch–oil composite dry film lubricants was investigated as a function of starch type (waxy vs. normal purified food grade corn starch), oil chemistry (hexadecane vs. oleic acid and various vegetable oils), and starch‐to‐oil ratio. Based on the results, a mechanism of starch–oil interaction in these composites was proposed. According to the proposed mechanism: (a) the oil in the composite is distributed between the bulk and the surface of the starch; and (b) the fraction of the oil trapped in the bulk and that adsorbed on the surface are related to each other by an equilibrium constant, and are functions of the total oil concentration in the composite. In line with the proposed mechanism, an adsorption model was used to quantify the free energy of adsorption (ΔG_ads) of the polar oils onto the starch surface. The analysis gave ΔG_ads values that were higher than those reported for the adsorption of the same polar oils onto steel surfaces. This result is consistent with the effect of the relative surface energies of steel and starch on the adsorption of polar oils. The adsorption property of the non‐polar hexadecane relative to the polar oils was estimated by comparing their interfacial tensions with starch. The result showed a higher interfacial tension for hexadecane–starch than that for the polar oil–starch composites. This result predicts a relatively poorer compatibility with, and, hence, poorer adsorption of hexadecane onto starch leading to higher COF, as was observed in the friction measurements. Published in 2006 by John Wiley & Sons, Ltd.     

Maltenes and Asphaltenes of Petroleum Vacuum Residues: Physico-Chemical Characterization

Solvent separation is frequently applied to petroleum vacuum residues to reduce the coke-forming tendencies of these materials. This process is capable of removing all or a substantial amount of asphaltenes from feedstocks that are destined for further processing and thus applied as the first step of refining. Maltenes and asphaltenes obtained from vacuum residues of Heera (HVR) and Jodhpur (JVR) Indian crude oils using n-hexane, n-heptane, and soluble and insoluble fractions obtained using ethyl acetate, were characterized for elemental analysis, molecular weight, conradson carbon residue (CCR), specific gravity, and pour points. The resulting degree of removal of asphaltenes ranged from 10-28 wt% of the HVR and 25-50 wt% of the JVR. The increasing trend of the American Petroleum Institute (API) gravity and the decreasing trend of CCR and pour point are observed with the increase in removal of asphaltenes.     

A Multivariate Subgroup Rationality Test

In one of our recent articles (Holmes, D. S., Mergen, A. E. (2003). Testing rationality of subgroups in multivariate control charts. In: The 2003 Northeast Decision Sciences Institute Meeting Proceedings. Providence, Rhode Island, March 27-29, Fariborz Partovi, 286-288.) we proposed an aggregate measure for checking rationality of the subgroups in multivariate control charts, such as T² charts. The purpose of this article is to build on that measure and propose a similar multivariate test to check the rationality of each subgroup used in the chart. The proposed test uses the statistical process control (SPC) approach; i.e., maintains the time sequence of the data. The method is based on a test for equality of two covariance matrices (Kramer, C. Y., Jensen, D. R. (1969). Fundamentals of multivariate analysis—part II: inference about two treatments. Journal of Quality Technology 1(3):189-204.). The first covariance matrix is the one normally described in statistical literature (for example Johnson and Wichern (Johnson, R. A., Wichern, D. W. (1992). Applied Multivariate Statistical Analysis. New Jersey: Prentice Hall 92-122.) The second matrix used in the test is the multivariate mean square successive difference (MSSD) covariance matrix (Holmes, D. S., Mergen, A. E. (1993). Improving the performance of T-square control chart. Quality Engineering 5(4):619-625.). If the test indicates a significant difference of these two matrices, this is an indication of the lack of rationality of the corresponding subgroup(s) being used on the multivariate control chart. The test result for each subgroup can then be plotted on a control chart to explore which subgroup(s) may be the cause of the nonrationality. Two examples of the use of the proposed method are given.     

A new arc detection method based on fuzzy logic using S-transform for pantograph–catenary systems

pantograph–catenary system is one of the critical components used in electrical trains. It ensures the transmission of the electrical energy to the train taken from the substation that is required for electrical trains. The condition monitoring and early diagnosis for pantograph–catenary systems are very important in terms of rail transport disruption. In this study, a new method is proposed for arc detection in the pantograph–catenary system based signal processing and S-transform. Arc detection and condition monitoring were achieved by using current signals received from a real pantograph–catenary system. Firstly, model based current data for pantograph–catenary system is obtained from Mayr arc model. The method with S-transform is developed by using this current data. Noises on the current signal are eliminated by applying a low pass filter to the current signal. The peak values of the noiseless signals are determined by taking absolute values of these signals in a certain frequency range. After the data of the peak points has been normalized, a new signal will be obtained by combining these points via a linear interpolation method. The frequency-time analysis was realized by applying S-transform on the signal obtained from peak values. Feature extraction that obtained by S-matrix was used in the fuzzy system. The current signal is detected the contdition as healthy or faulty by using the outputs of the fuzzy system. Furthermore the real-time processing of the proposed method is examined by applying to the current signal received from a locomotive.     

The Effects of Structural,Thermal, and Magnetic Properties of Hexylbenzene-Doped MgB<Subscript>2</Subscript> Superconductor

The effects of the amount of hexylbenzene additive (C₁₂H₁₈) on the structural, thermal, and magnetic properties of MgB₂ superconductor are examined in this study. Pure and hexylbenzene-doped MgB₂ bulk samples were produced with in situ solid-state reaction method. X-ray diffraction patterns of MgB₂ doped with MgB₂ and hexylbenzene at different ratios were determined to have MgB₂ as the main phase and consisted of a small amount of MgO. Pure and different ratios of hexylbenzene-doped Mg and B starting powders were heat-treated by a differential scanning calorimeter between room temperature and 800 °C. It was determined from the differential scanning calorimetry curves obtained that the first exothermic peak pointed the MgB₂ phase emerging with a solid–solid (Mg–B) reaction, and this temperature shifted towards the low temperatures as the hexylbenzene addition rates increased. It was observed that there was dependency to the applied field in all samples from the ac susceptibility measurements as a function of the temperature in pure and hexylbenzene-doped MgB₂ superconductor materials, and shift towards the lower temperatures in T _c, superconducting transition temperature, with increasing content. It was observed that the changes occurred in in-phase (\(\chi ^{\prime })\) and out-off-phase (\(\chi ^{\prime \prime }\)) components of ac susceptibility both weakened the MgB₂ phase structure of hexylbenzene content and, as a result of this, led to changes in the pinning mechanism.     

Role of Aniline Addition in Structural and Superconducting Properties of MgB<Subscript>2</Subscript> Bulk Superconductor

In this study, the structural and superconducting properties of aniline-added MgB₂ superconductors were investigated by X-ray diffraction (XRD), thermal analysis techniques, and ac susceptibility measurements. The amount of aniline was changed from 0 to 1 mol%. Phase analysis and lattice parameters were determined from XRD measurements. X-ray diffraction analysis indicates that the main phase is MgB₂ and that there is a small amount of Mg as the secondary phase in aniline-added samples. According to the determination of lattice parameters, it is seen that the addition of aniline does not give a proper distribution with the contribution amount of a and c lattice parameters. From DSC curves, two exothermic peaks and one endothermic peak were observed in all samples. Pure and aniline-added samples were found to be dependent on the magnetic field in the ac susceptibility measurements, and the superconducting transition temperature (T _c ) was found to decrease to lower temperatures due to an increase in the amount of aniline. It has been determined that changes in the in-phase (χ ^′) and out-of-phase (χ ^″) components of the ac susceptibility by increasing the aniline amount have weakened the MgB₂ phase structure and thus cause changes in the pinning mechanism. In addition, ac losses of all the samples were calculated under external fields ranging from 160 to 1280 A/m and at 25 K.