Alumina Dissolution into Silicate Slag

Dissolution of commercial white fused and tabular Al₂O₃ grains into a model silicate slag was investigated after 1 h at 1450° and 1600°C. Formation of CA₆ and hercynitic spinel layers was observed at all Al₂O₃/slag interfaces. The spinel layer was not always continuous, and so, compared with the CA₆ layer, it had a less-significant effect on the dissolution process. The CA₆ layer that formed adjacent to the tabular Al₂O₃ was incomplete at both temperatures, so that its dissolution was not a totally indirect process. These incomplete CA₆ and spinel layers meant that slag penetrated into the tabular Al₂O₃ grains, which, thus, were corroded and disintegrated by the penetrating slag. There was evidence of liquid in the CA₆ layer adjacent to the fused Al₂O₃ after 1 h at 1450°C, which also enabled direct dissolution. After 1 h at 1600°C, fused Al₂O₃ revealed a thick (∼60 μm), continuous and unpene-trated CA₆ layer, indicating fully indirect dissolution at this temperature.     

Fourier transform infrared spectroscopic and AC electrical conductivity studies of chitin and its derivatives

The vibrational modes and the purity index of chitin and its derivatives as biopolymers are studied by Fourier transform infrared spectroscopy in the wavenumber range from 4000 to 400 cm^?1. The absorption bands of chitin and its derivatives are assigned. New bands appeared at 1419, 1209, 915, and 800 cm^?1 for chitin derivatives due to the change of vibrational modes. The purity indexes are calculated from the ratio of the absorption band of C = O at 1662 cm^?1 and OH at 3443 cm^?1. Generally, the purity indexes of chitin derivatives are higher than that of chitin, which is due to the decrease of OH. The dielectric properties such as the real part of the dielectric constant (ε′) and loss tangent tan (δ) are measured as a function of temperature at different frequencies ranging from 200 to 2000 kHz. The increase of (ε′) and tan (δ) with increasing temperature is discussed on the basis of increasing polarizability and the decrease with increasing frequency can be attributed to the dielectric dispersion. AC electrical conductivities as a function of the reciprocal of the absolute temperature are also discussed. The mechanism of the charge carrier is discussed as a tunneling model in the temperature range from 300 to 360 K. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 936–943, 2005     

Crosslinking of ethylene propylene diene monomer (EPDM) by buckminsterfullerene

An EPDM (ethylene-propylene-ethylidene norbornene terpolymer) rubber has been dissolved in o-dichlorobenzene with 1 phr of C₆₀. When cast onto a glass slide and dried, an insoluble film exhibiting reversible elasticity forms. Received: 10 December 1996/Revised: 13 January 1997/Accepted: 17 January 1997     

Coordinated tuning of power system stabilizers in multimachine power systems

In this paper a new approach to simultaneously tuning the power system stabilizer (PSS) settings in a multimachine electric utility system is presented. The approach is based on eigenvalue assignment, which is treated as a problem of solving a set of non-linear equations. The possibility of meeting additional specified performance criteria is discussed. The flexibility of the proposed method is demonstrated using an operating utility system.     

The effect of SiO2 additions on barium aluminate cement formation and properties

Barium aluminate cements have been synthesized by barium carbonate, alumina, kaolin and colloidal silica as starting materials. The effects of the source of SiO₂ and of firing temperature on phase formation and physical properties of the fired cements have been studied. Cement samples were characterized using XRD, SEM, EDX. The setting time and heat of hydration of cements were also evaluated. The barium aluminate cements were mixed in castables. Cold crushing strengths evaluated, and values compared to those obtained using calcium aluminate cement (Secar 71). Mixtures of BaCO₃ and Al₂O₃ were targeted to produce BaAl₂O₄; which had fast set time, expansive behavior and lower strength compared to samples with SiO₂ additions. SiO₂ additions, regardless of source, resulted in BaAl₂Si₂O₈ (celsian) formation. The prepared samples had short setting times and higher mechanical properties in comparison with standard calcium aluminate cement.     

Diagnosis of attention deficit hyperactivity disorder using non‐linear analysis of the EEG signal

Attention deficit hyperactivity disorder (ADHD) is a common behavioural disorder that may be found in 5%–8% of the children. Early diagnosis of ADHD is crucial for treating the disease and reducing its harmful effects on education, employment, relationships, and life quality. On the other hand, non‐linear analysis methods are widely applied in processing the electroencephalogram (EEG) signals. It has been proved that the brain neuronal activity and its related EEG signals have chaotic behaviour. Hence, chaotic indices can be employed to classify the EEG signals. In this study, a new approach is proposed based on the combination of some non‐linear features to distinguish ADHD from normal children. Lyapunov exponent, fractal dimension, correlation dimension and sample, fuzzy and approximate entropies are the non‐linear extracted features. For computing, the chaotic time series of obtained EEG in the brain frontal lobe (FP1, FP2, F3, F4, and Fz) need to be analysed. Experiments on a set of EEG signal obtained from 50 ADHD and 26 normal cases yielded a sensitivity, specificity, and accuracy of 98, 92.31, and 96.05%, respectively. The obtained accuracy provides a significant improvement in comparison to the other similar studies in identifying and classifying children with ADHD.Inspec keywords: feature extraction, time series, fractals, electroencephalography, medical disorders, neurophysiology, medical signal processing, entropy, signal classification, Lyapunov methodsOther keywords: nonlinear extracted features, chaotic time series, identifying classifying children, attention deficit hyperactivity disorder, nonlinear analysis methods, electroencephalogram signals, brain neuronal activity, chaotic behaviour, chaotic indices, EEG signals, nonlinear features, approximate entropies, common behavioural disorder, early diagnosis, life quality, ADHD     

Dynamic properties of calcareous and siliceous sands under isotropic and anisotropic stress conditions

The strain-dependent dynamic properties of sand are generally described by their relative density and mean effective stress, while the contribution of other factors, like soil origin, mineralogy, grain morphology, and initial stress anisotropy, have not been fully recognized. This paper presents the results of an experimental study on the shear modulus and damping ratio of calcareous and siliceous sands of different origins and their identical grain size distribution and stress-density states. Resonant column and cyclic triaxial tests were conducted on reconstituted samples of these two sands obtained from coastal areas. The significance of the initial effective confining pressure and stress anisotropy on the dynamic properties of the sands is evaluated and compared. It is demonstrated that the small-strain shear modulus of the calcareous sand is more affected by an increase in mean effective confining pressure than the siliceous sand. However, the effect of the initial shear on the secant shear modulus of the sands is unique. Based on the test data, a rigorous correction factor is proposed to account for the influence of the initial stress anisotropy on the small-strain shear modulus of the sands. A comparison between the strain-dependent dynamic properties of the calcareous and siliceous sands reveals that the calcareous sand has a higher secant shear modulus, lower damping ratio, and higher linear and volumetric threshold strain. Since the stress-density states and grain size distribution of the two sands were identical in the experiments, the discrepancy in the dynamic properties can be attributed to other factors, including sand origin, grain angularity, mineralogy, and formation processes, which are not commonly taken into account in the current practice.     

Eutectic Morphology in Alloy Pb – 3.2% Cd – 0.08% Sr for Battery Grids

Metal Science and Heat Treatment - Ageing of supersaturated solid solution in Pb – 3.2% Cd – 0.08% Sr alloy is studied at 20 and 80°C by measuring hardness, and light and scanning...     

Radon emanation from radium specific adsorbents

Pilot studies were undertaken to quantify the total activity of radon that is eluted following no-flow periods from several Ra-226 adsorbents loaded to near exhaustion. The adsorbents studied included two types of barium sulphate impregnated alumina (ABA-8000 and F-1) and Dowex MSC-1 resin treated by either barium hydroxide or barium chloride. In parallel, radium loaded plain activated aluminas and Dowex MSC-1 resin were similarly investigated. The results revealed that radon was quantitatively eluted during the first few bed volumes of column operation after no-flow periods. Although similar radon elution profiles were obtained, the position of the radon peak was found to vary and depended on the adsorbent type. Radon levels up to 24 and 14 kBq dm⁻³ were measured after a rest period of 72 h from radium exhausted Dowex MSC-1 treated with barium chloride and F-1 impregnated alumina with barium sulphate, respectively. The eluted radon values measured experimentally were compared to those calculated theoretically from accumulated radium quantities for the different media. For plain adsorbents, an agreement better than 10% was obtained. For treated resin-types a consistency within 30% but for impregnated alumina-types high discrepancy between respective values were obtained.