Aqueous sol–gel synthesis of zirconium titanate (ZrTiO4) nanoparticles using chloride precursors

Zirconium titanate powders were synthesized by a straightforward sol–gel method using zirconium and titanium chlorides as metal precursors, deionized water as solvent and oxygen donor, and a NaOH solution for adjusting pH to 7. According to transmission electron microscopy, amorphous particles of nearly 5 nm in size with a relatively spherical morphology were prepared. Thermogravimetry and differential scanning calorimetery analyses on the xerogel at a heating rate of 10 °C/min indicated a crystallization temperature of 690 °C, which is comparable with previous reports. Furthermore, via differential scanning calorimetery studies using the Kissinger's equation, the activation energy for ZrTiO₄ crystallization was determined to be 850 kJ/mol. Structural evaluations in the isothermal regime, using X-ray diffraction experiments, implied the onset of ZrTiO₄ crystallization at 550 °C.     

27—THE NORMAL FORCE BETWEEN TWISTED FILAMENTS: PART II: EXPERIMENTAL VERIFICATION

In a previous paper, the importance of lateral pressure in the tension and bending behaviour of yarns was discussed; a theoretical model, which included the effects of bending and torsional rigidities as well as the tensile, shear, and frictional forces, was proposed, and expressions for the lateral pressures were derived. In this sequel, the experimental verification of the previously derived expressions has been carried out on a very simple twisted structure, consisting of two rubber strands. The results obtained support the theoretical predictions of the lateral pressure for the experimental model and lead to the conclusion that, for filaments with significant torsional and bending rigidities, lateral pressures are obtained in the yarn even when there is no significant tension on the individual filaments. An approximate scheme for estimating the lateral pressures in an idealized, close-packed, multilayered continuous-filament yarn is proposed as an extension of the above results.     

Iterative learning control for non-linear systems described by a blended multiple model representation

This paper deals with the design of gain-scheduling-based iterative learning controllers for continuous-time non-linear systems described by a blended multiple model representation. Sufficient conditions guaranteeing the convergence of the infinity norm as well as the u -norm of the tracking error are derived. The effectiveness of the proposed control scheme is illustrated on an example of a non-affine-in-input system.     

All-pass filtering in iterative learning control

In iterative learning control (ILC), it is highly desirable to have a learning compensator with a unit-gain for all frequencies, in order to avoid noise amplification and learning speed degradation during the learning process. In this paper, we show that the realization of a unit-gain compensator is straightforward in ILC, using both forward and backward filtering. As an illustrative example, a unit-gain derivative is proposed to overcome the drawbacks of the conventional derivative. The proposed scheme is equivalent to an all-pass unit-gain phase shifter; the forward filtering uses a 0.5-order derivative and the backward filtering employs a 0.5-order integral. The all-pass phase shifter is deployed in a unit-gain D-type ILC. The advantages of the unit-gain feature are demonstrated by some experimental results on a robot manipulator.     

MEASUREMENT TECHNIQUES AND DATA INTERPRETATIONS FOR VALIDATING CFD MULTI PHASE REACTOR MODELS

One problem associated with the use of Computational Fluid Dynamics(CFD) in reactor modeling is the proper validation of the models. Proper validation in this context means that the physical fluid dynamic model, the mathematical implementation and the data used for validation must be consistent. The present paper addresses this issue and to provide appropriate relations between experimental method and modeling approach

A critical review of currently used measurement techniques for characterizing multiphase now systems is presented. The interpretation of the data obtained from the various techniques is discussed as well as how these data can be used for validation of various CFD model formulations

Steady state models can be validated using time averaged data, making sure that the averaging time for the experimental data is long enough so that low frequency periodic oscillations also are evened out. If homogeneous systems are considered, then a volume average approach may be used for modeling, If the system cannot be considered homogeneous and steady, as is the most common case, then a dynamic ensemble averaging technique should be preferred. The validation of such models must be done with methods fast enough to resolve periodic fluctuating structures of interest. These methods are cumbersome and tedious to operate and the ergodic hypothesis may be invoked enabling the use of volume or time averaged data for the validation of ensemble averaged models.     

Study of 55Al-43.6Zn-1.6Si Alloy Coating Parameters over St37 Steel Sheet via Hot-Dipping Process and its Corrosion Behavior

In this work the 55Al-43.4Zn-1.6Si alloy coating produced by hot-dipping technique was studied. The St37 steel sheets were coated through dipping in the molten at different bath temperature and various dipping time. Microstructure of the coatings was evaluated using Optical Microscope (OM) and Scanning Electron Microscope (SEM). Elemental analysis of the specimens was investigated by the Energy Dispersive X-ray Spectroscopy (EDX) analysis. The results showed that, by increasing the bath temperature, the thickness of the both coating (55Al-43.4Zn-1.6Si) and the intermetallic layer (Fe₄Al₁₃) increased. The results revealed that, the growth rate of the intermetallic layer was much lower than that of the coating. Adhesiveness and hardness of the coating evaluated by the bending and Vickers microhardness tests. The hardness results showed that by increasing the temperature and duration time, the hardness of the coating was decreased. Additionally, flexibility of the coatings in the all three different temperatures of the molten bath was slightly decreased. Salt spray test was used to study the corrosion behavior of the coatings. Results showed that the specimens coated at 650 ^°C for 60 s revealed the best performance in the salt spray test.     

Genotypic heterogeneity and phenotypic variation among patients with type 2 Gaucher''s disease

Electrophysiological examination of the function of perceptive organs, like eye or cochlea, works up more and more interest in scientists to look for an objective method of vestibular end organ investigation. In many papers authors attempt to estimate the efficiency of vestibular organs after using angular or linear acceleration as stimulus, which required special and expensive apparatus. Papers that described vestibular evoked myogenic potentials (VEMPs) seem to be very promising. In this study an attempt was taken to obtain VEMPs with own modification of stimulus and response register. Preliminary examinations in 14 healthy volunteers were performed. Two subjects with sensorineural deafness on one side and symmetric, normal excitability of vestibular organs and 4 with bilateral hearing loss and unilateral weakness of vestibular excitability were examined. There were also 6 patients with only weakness of vestibular excitability. On the basis of practical observations, there is a possibility that evoked potentials were a result of stimulation of vestibular part of the inner ear--sacculus. The method of the study is objective, simple, secure and comfortable for patients.     

Entropy generation analysis of convective airflow in a solar updraft tower power plant

The main objective of this numerical investigation is to interpret the entropy generation for free convection airflow in a solar tower updraft system. The ground surface is subjected to uniform hot temperature and the collector cover is maintained at lower constant temperature while the chimney wall is adiabatic. Two dimensionless equations of steady laminar free convective airflow are discretized using the finite volume approach. Numerical solutions were accomplished for different values of the Rayleigh number. Results are given in terms of isotherms, velocity magnitude, local entropy generation associated with thermal and fluid friction, local total entropy generation and local Bejan number contours for Rayleigh number ranging between 10³ and 10⁸. The reported results show that thermal and frictional irreversibilities are proportional to the Rayleigh number. Also, it was found that, at lower Rayleigh, total irreversibility is attributable to the thermal irreversibilities and occurs essentially in the collector section. At higher Rayleigh, frictional irreversibilities are increased significantly and become the dominant source of irreversibility in the solar tower, and the chimney section is the main contributor in the total irreversibility in the system.