Rigorous Results on Surface Diffusion Coefficients Near a First-Order Phase Transition

We present a microscopic statistical–mechanical approach from which the chemical surface diffusion coefficient can be obtained in the local equilibrium limit, assuming that the system of a finite size undergoes a first-order phase transition between two phases. We also show the behavior of the jump diffusion coefficient and thermodynamic factor near such a transition. Explicit formulas for the dependences of these quantities on the chemical potential, coverage, and size of the system are presented. The general results are applied to a simple two-dimensional lattice model on a regular triangular lattice.     

Changes in microfibril angle in cyclically deformed dry coir fibers studied by in-situ synchrotron X-ray diffraction

Dry coir fibers are characterized by wide-angle X-ray scattering coupled with tensile tests. The fibers exhibit elastic and plastic behavior with the yield point at a strain of about 2%. In-situ experiments document that the cyclic loading and unloading beyond the yield point does not reduce the stiffness of the fibres, since they recover their initial stiffness by every increase of the strain. The diffraction data show that the microfibril angle (MFA) of cellulose fibrils in the coir fibre cells is inversely proportional to the magnitude of the applied strain. In average, the relatively high MFA of about 45° in the unstrained state decreases linearly upon straining until the fibers break at about 35% strain. When the strain is released during the tensile experiment the MFA tends to recover its original magnitude. No significant differences in the dependence of MFA on strain are detected in elastic and plastic regions, respectively. The results demonstrate that the tissue with helical architecture does not have to be saturated with water in order to exhibit the effect of the recovery of the mechanical function when cyclically loaded. This indicates differences in the architecture of the coir cell wall in comparison with that of compression wood with high MFA whereby similar phenomena were observed in the wet state.     

Preparation of ω-hydroxynonanoic acid and its ester derivatives

Methyl ricinoleate was ozonized in methanol or in acetic acid and the intermediate hydroperoxides were reduced electrochemically on Pb-cathode to give 9-hydroxynonanoic acid 1 in high yields. The acid 1 was also prepared by direct castor oil ozonolysis in methanol followed by sodium borohydride reduction of the intermediate hydroperoxides. The cost of the electricity for the electroreduction was at least 30 times lower as compared with sodium borohydride consumption. 9-Hydroxynonanoic acid was then transformed to alkyl 9-acetoxynonanoates 3a–3d, for which ¹H nuclear magnetic reasonance, mass, and infrared spectra are given. Esterification of the hydroxy acid 1 with boric acid and pyrolysis of the resultant orthoborates produced 8-nonenoic acid 4 in a 45% yield. Reaction of 4 with lower aliphatic alcohols in presence of Amberlyst 15 produced alkyl 8-noneates 5a–5d along with some amounts of a cis/trans mixture of alkyl 7-noneates.     

Effect of a gas–liquid separator on the hydrodynamics and circulation flow regimes in internal‐loop airlift reactors

The role of the gas–liquid separator on hydrodynamic characteristics in an internal‐loop airlift reactor (ALR) was investigated. Both gas holdup and liquid velocity were measured in a 30 dm³ airlift reactor with two different head configurations: with and without an enlarged separator. A magnetic tracer method using a neutrally buoyant magnetic particle as flowfollower was used to measure the liquid velocity in all sections of the internal‐loop airlift reactor. Average liquid circulation velocities in the main parts of the ALR were compared for both reactor configurations. At low air flow rates the separator had no influence on gas holdup, circulation velocity and intensity of turbulence in the downcomer and separator. At higher superficial air velocities, however, the separator design had a decisive effect on the hydrodynamic parameters in the downcomer and the separator. On the other hand, the gas holdup in the riser was only slightly influenced by the separator configuration in the whole range of air flow. Circulation flow regimes, characterising the behaviour of bubbles in the downcomer, were identified and the effect of the separator on these regimes was assessed. © 2001 Society of Chemical Industry     

Properties of polyethersulfone ultrafiltration membranes modified by polyelectrolytes

This study reports on the surface modification of ultrafiltration membranes using the layer-by-layer (LbL) technique. The novelty of this work resides in the LbL assembly of charged polyelectrolytes by electrostatic adsorption directly onto the ultrafiltration membranes without any prior treatment of the surface. Polyethersulfone ultrafiltration membranes have been employed for the deposition of branched poly(ethyleneimine) and poly(sodium 4-styrene sulfonate) to create a thin polyelectrolyte film on their surface. The modified membranes are characterized by their permeability and molecular weight cut-off (MWCO) value. Experiments show that the deposited polyelectrolyte layer causes a decrease in the permeability due to the additional resistance of the layers. However, the MWCO value is shifted meaning a better rejection of the dextran solution is achieved. Thus, the LbL assembly of polyelectrolyte multilayers on the surface of the membrane makes it possible to convert a membrane with open structure to a membrane with denser active layer.     

An Approach to Platform Independent Real-Time Programming: (2) Practical Application

In a previously published companion paper a method for extending programming languages with timing constructs was proposed. It was shown that the extension enables the construction of real-time programs that can be proven correct independently of the properties of the machine that is used for their execution. It also yields a strict division of system construction into two phases: (1) a platform-independent programming phase that includes the expression of timing requirements, and (2) an implementation phase where all platform dependencies are addressed. In this second paper the approach is illustrated using an example problem often quoted in the literature: the mine-pump system. The two mentioned phases are described in detail for this example. First, a program is obtained in a systematic way. Then, realizations of the program under various schemes for distribution and scheduling are considered and analyzed. A comparison with other approaches to real-time programming is given.     

Tribological Properties of TiN/Ag Nanocomposite Coatings

Morphology, structure, and tribological behavior of magnetron co-sputtered TiN/Ag nanocomposite coatings deposited at 150 °C with an Ag content in the range of 7–45 at.% were characterized. The coatings show a columnar structure with embedded Ag crystallites of 3–50 nm in diameter, where the columns are characterized by a layered structure with Ag-poor and Ag-rich layers. These layers originate from sample rotation during deposition, where the layer thickness increases with increasing Ag content. These Ag layers become continuous over a critical Ag content. At room temperature the friction coefficient is determined by the film structure, whereas friction and wear at high temperature depend on segregation of Ag to the surface.     

Effect of vanadium on grain boundary segregation of phosphorus in low alloy steels

The phosphorus grain boundary segregation at 853 K was investigated in three low alloy steels with different vanadium content. Kinetic dependence of the phosphorus grain boundary concentration was determined experimentally by means of AES and described theoretically, as well. To assess the influence of the individual alloying elements on the phosphorus segregation, the metal composition of carbide phases at 853 K was predicted by means of thermodynamic calculations and confirmed by experimental measurements (TEM + EDX). The vanadium was found to enhance the phosphorus grain boundary segregation by reducing the amount of dissolved and segregated carbon. Thereby, the equilibrium of mutual displacement C (segregated) ? P (segregated) was shifted to more phosphorus segregation. The results achieved indicate that vanadium indirectly increases sensitivity of low alloy steels to intergranular embrittlement.     

Exploiting quantization and spatial correlation in virtual-noise modeling for distributed video coding

Aiming for low-complexity encoding, video coders based on Wyner–Ziv theory are still unsuccessfully trying to match the performance of predictive video coders. One of the most important factors concerning the coding performance of distributed coders is modeling and estimating the correlation between the original video signal and its temporal prediction generated at the decoder.One of the problems of the state-of-the-art correlation estimators is that their performance is not consistent across a wide range of video content and different coding settings. To address this problem we have developed a correlation model able to adapt to changes in the content and the coding parameters by exploiting the spatial correlation of the video signal and the quantization distortion.In this paper we describe our model and present experiments showing that our model provides average bit rate gains of up to 12% and average PSNR gains of up to 0.5 dB when compared to the state-of-the-art models. The experiments suggest that the performance of distributed coders can be significantly improved by taking video content and coding parameters into account.     

Catalytic and thermal cracking of selected polyolefins

Feedstock recycling is a promising alternative for the management of plastic wastes, as it may allow these residues to be transformed into valuable products for refinery and/or petrochemical industry. Catalytic degradation of polyolefin was carried out in a pilot scale reactor Blowdec® operating in the temperature range of 340–470°C. The catalysts used in this study were natural zeolite Clinoptilolite, ZSM-5, HZSM-5 and their mixture in various volume ratios. Both thermal and catalytic cracking of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and their mixture have been investigated. Liquid products were checked in selected refinery and petrochemical processes as feedstocks on the model pyrolysis equipment and with the help of MAT test (microactivity test).