Aspects of the chemistry of poly(ethylene terephthalate): 5. Polymerization of bis(hydroxyethyl)terephthalate by various metallic catalysts

Bis(hydroxyethyl)terephthalate (BHET) was polymerized to poly(ethylene terephthalate) (PET) in the presence of various metallic catalysts. The influence of the nature and concentration of these catalysts on the rate of polymerization has been investigated. The effect of the reaction temperature has also been studied. The order of decreasing catalytic influence of various metal ions, on the polymerization of BHET was found to be: Ti>Sn>Mn>Zn>Pb>No.     

In situ TiC-reinforced austenitic steel composite by self-propagating high temperature synthesis

TiC-reinforced austenitic steel composites have been prepared by self-propagating high temperature synthesis (SHS). The in situ reinforcement of a Fe-Mn-based austenitic steel matrix with TiC was achieved upon aluminothermic reduction of iron oxide (Fe₂O₃), manganese dioxide (MnO₂) and titanium dioxide (TiO₂) powders in the presence of carbon (C). This highly exothermic thermite reaction was found to produce in situ the Fe-Mn-TiC austenitic steel composites. The reaction kinetics, recovery of Mn and TiC, yield of metal, and composite microstructure were found to strongly depend on the process parameters, such as green composition, blending sequence, and average particle size of Al powder used as a reducing agent. The text was submitted by the authors in English.     

Kinetics of organic sulphur removal from coal by oxydesulphurization

This paper presents some experimental data for the kinetics of organic sulphur removal from Lower Freeport coal by oxidation in an aqueous medium. The experimental data were obtained in a semi-batch (gas flow, no flow of slurry) agitated reactor for the ranges of temperature 403–473 K, oxygen partial pressure 0.32–1.36 MPa, solids loading 3–26 wt%, average coal particle size 75–955 μm and time 0–5400 s. The experimental data were taken under acidic, neutral and alkaline conditions. The results indicate that under acidic conditions, no organic sulphur was removed at moderate and low pressures and temperatures. Whenever significant organic sulphur was removed, the removal rate followed first-order kinetics with respect to the organic sulphur. Under otherwise identical conditions, the organic sulphur removal increased with the pH of the aqueous medium.     

Erratum to: An analysis on decentralized adaptive MAC protocols for cognitive radio networks

正Erratum to:International Journal of Automation and Computing DOI:10.1007/s11633-013-0695-z The original version of this article unfortunately contained a mistake.The received date and revised date were incorrect.The corrected received date and revised date are given below.     

Mass transfer with chemical reaction in liquid foam reactors

Mass transfer studies were conducted in a stable liquid foam reactor under various operating conditions to evaluate gas holdup, effective interfacial area, liquid-phase mass transfer coefficient and a modified interfacial mass transfer coefficient to include the surface-active agents employed. Gas holdup and effective interfacial area were evaluated experimentally. The interfacial mass transfer coefficient was evaluated semitheoretically, by considering the interfacial region as a separate phase and using the experimental data developed for mass transfer accompanied by a fast first-order chemical reaction. The liquid-phase mass transfer coefficient was also evaluated semitheoretically, using Danckwert's theory for the liquid phase and the experimental data on mass transfer accompanied by a slow pseudofirst-order chemical reaction. An experimental unit was set up to provide a stable flowing foam column, simulating the foam reactor. Mass transfer rates were studied for superfacial gas velocities in the range from 1.5 × 10⁻² m/s to 5 × 10⁻² m/s, giving gas residence times in the range from 20 to 55 seconds. A cationic and nonionic surface-active agent and three different wire mesh sizes, giving bubble size distributions in the range from 2.2 to 5.4 mm Sauter mean diameters, were employed. It is observed that gas holdup is insensitive to the type of surface-active agent; it is however, dependent on wire mesh size and gas velocity. The bubble diameter and, hence, the interfacial area are found to be insensitive to gas velocity in the range studied; they are, however, strong functions of wire mesh size. The liquid-phase mass transfer coefficient increases with increase in gas velocity. The surface-active agent introduces additional resistance to mass transfer in both reaction cases, this being the controlling one in the case of the fast reaction. A comparison with conventional packed bed contactors indicates the mass transfer rates to be about 8 times lower for the foam reactor, for the fast reaction case; for slow reactions, the foam reactor has mass transfer rates approximately 2-4 times higher than those for conventional packed bed contactors.     

Nylon 6 nanocomposites prepared by a melt mixing masterbatch process

A melt mixing masterbatch process for preparing nylon 6 nanocomposites that provides good exfoliation and low melt viscosities has been investigated. It is known that high molecular weight (HMW) grades of nylon 6 lead to higher levels of exfoliation of organoclays than do low molecular weight (LMW) grades of nylon 6. However, LMW grades of nylon 6 have lower melt viscosities, which are favorable for certain commercial applications like injection molding. To resolve this, a two-step process to prepare nanocomposites based on nylon 6 is explored here. In the first step, a masterbatch of organoclay in HMW nylon 6 is prepared by melt processing to give exfoliation. In the second step, the masterbatch is diluted with LMW nylon 6 to the desired montmorillonite (MMT) content to reduce melt viscosity. Wide angle X-ray scattering, transmission electron microscopy, and stress-strain analysis were used to evaluate the effect of the clay content in the masterbatch on the morphology and physical properties of the final nanocomposite. The melt viscosity was characterized by Brabender Torque Rheometry. The physical properties of the nanocomposites prepared by the masterbatch approach lie between those of the corresponding composites prepared directly from HMW nylon 6 and LMW nylon 6. A clear trade-off was observed between the modulus and melt processability. Masterbatches that have lower MMT content offer a significant decrease in melt viscosity and a small reduction in modulus compared to nanocomposites prepared directly from HMW nylon 6. Higher MMT concentrations in the masterbatch lead to a less favorable trade-off.     

A biorepository for ophthalmic surgical specimens

Biorepositories are collections of surgically obtained human tissues for current and future investigations of disease mechanisms, therapeutics, and diagnostics. In ophthalmology, a critical challenge is how to interface the operating room with the laboratory. To attain standards required for basic research, clinical and research teams must cooperate to collect, annotate, and store specimens that yield consistent results required for advanced molecular techniques. We developed an efficient platform for obtaining vitreous and other eye tissues from the operating room and transferring them to the lab. The platform includes a mobile lab cart for on-site tissue processing, a multi-user, web-based database for point-of-care phenotypic capture, and an integrated data tracking system for long-term storage. These biorepository instruments have proven essential for our studies in ophthalmic disease proteomics. This system can be implemented in other operating rooms and laboratories for a variety of biological tissues.     

Botnet detection techniques: review,future trends,and issues

In recent years, the Interact has enabled access to widespread remote services in the distributed computing environment; however, integrity of data transmission in the distributed computing platform is hindered by a number of security issues. For instance, the botnet phenomenon is a prominent threat to Intemet security, including the threat of malicious codes. The botnet phenomenon supports a wide range of criminal activities, including distributed denial of service （DDoS） attacks, click fraud, phishing, malware distribution, spam emails, and building machines for illegitimate exchange of information/materials. Therefore, it is imperative to design and develop a robust mechanism for improving the botnet detection, analysis, and removal process. Currently, botnet detection techniques have been reviewed in different ways; however, such studies are limited in scope and lack discussions on the latest botnet detection techniques. This paper presents a comprehensive review of the latest state-of-the-art techniques for botnet detection and figures out the trends of previous and current research. It provides a thematic taxonomy for the classification of botnet detection techniques and highlights the implications and critical aspects by qualitatively analyzing such techniques. Related to our comprehensive review, we highlight future directions for improving the schemes that broadly span the entire botnet detection research field and identify the persistent and prominent research challenges that remain open.     

An audit of cardiac pacing in the elderly: effect of myocardial infarction on outcome

OBJECTIVE: To audit the outcome of temporary endocardial pacing in an elderly population. DESIGN: Retrospective case-series analysis. SETTING: The Department of Medicine for the Elderly at the Wrexham Maelor Hospital, a District General Hospital with 612 beds serving a catchment population of 220,000. SUBJECTS: A sample of 50 consecutive elderly patients, with an age range of 65 to 99 years, undergoing transvenous cardiac pacing. MAIN OUTCOME MEASURES: Length of stay in hospital, complications of the pacing procedure, whether a permanent pacemaker was installed, and whether the patient died within 1 month of admission. RESULTS: There was no difference in length of stay between those with a myocardial infarction and those without. Minor complications occurred in three patients (one local infection and two "failures to pace"). Major complications occurred in two patients (septicemia and pneumonia). More patients without a myocardial infarction (86.9%) went on to implantation of a permanent pacemaker than those with an infarction (11.1%, P = 0.001), and fewer of them died (8.7% compared with 48.1%, P = 0.0025). In those patients with a myocardial infarction who died, there was no difference between the proportions who had inferior (7/18) and anterior (5/9) infarctions. CONCLUSION: Cardiac pacing seems to be a safe and reliable procedure in the elderly, although long term morbidity and mortality may be dependent on the presence or absence of myocardial ischaemic disease. Myocardial infarction in the elderly is an event of major significance, carrying with it a high mortality rate, particularly if accompanied by cardiogenic shock and the need for cardiac pacing.