Characterization of various cement grinding aids and their impact on grindability and cement performance

The aim of the present research work was the evaluation of six commercial grinding additives, which were used for the production of Portland cement (ground in a ball mill at a laboratory stage). For this purpose, a reference sample was also produced without using any admixture. The characterization of the grinding aids (GA) was carried out by Fourier transform infra-red spectroscopy (FT-IR) and gas chromatography/mass spectrometry (GC/MS). All the cement mixtures were tested for initial and final setting times, consistency of standard paste, flow of normal mortar and compressive strengths after 2, 7 and 28 days. In all cases the addition of grinding aids resulted in improvement of the specific surface and grindability index, a fact that was attributed to the additive ability not only to reduce resistance to comminution, but also to prevent agglomeration and powder coatings of ball and mill. The mortars made with cements ground with the addition of commercial additives, which contained triisopropanolamine (TIPA), exhibited higher strength at any age and higher setting times. On the other hand, the presence of triethanolamine (TEA) on the commercial grinding additives did not affect the mechanical properties of the produced cements but slightly decreased their setting times.     

Exploiting agent mobility for large-scale network monitoring

As networks become pervasive, the importance of efficient information gathering for purposes such as monitoring, fault diagnosis, and performance evaluation increases. Distributed monitoring systems based on either management protocols such as SNMP or distributed object technologies such as CORBA can cope with scalability problems only to a limited extent. They are not well suited to systems that are both very large and highly dynamic because the monitoring logic, although possibly distributed, is statically predefined at design time. This article presents an active distributed monitoring system based on mobile agents. Agents act as area monitors not bound to any particular network node that can "sense" the network, estimate better locations, and migrate in order to pursue location optimality. Simulations demonstrate the capability of this approach to cope with large-scale systems and changing network conditions     

Using distributed object technologies in telecommunications networkmanagement

The Telecommunications Management Network (TMN) has been developed as the framework to support administrations in managing telecommunications networks. It suggests the use of OSI Systems Management (OSI-SM) as the technology for management information exchanges. Distributed object technologies, such as the Common Object Request Broker architecture (CORBA), address the use of software application program interfaces (APIs) in addition to interoperable protocols. Their use in TMN has been the subject of intensive research in previous years, with most approaches focusing on interoperability aspects with OSI-SM. We examine the issues behind using distributed object technologies in TMN via a native fashion, with network elements supporting distributed objects directly, e.g., a “CORBA to the switch” approach. The proposed solution tries to maintain the full OSI-SM expressive power in a way that other solutions have not attempted before. Performance and scalability issues are considered, while the approach has been validated through implementation     

Medical and safety monitoring system over an in-cabin optical wireless network

An integrated health and safety monitoring system for aircraft environments using commercially available medical sensor modules and custom made safety sensors in conjunction with an appropriate database supervised through a human–machine interface is implemented. The application described aims at preventing critical health- or safety-related situations during the flight. The health monitoring part of the system is capable of collecting all relevant data, essential in analysing a passenger's health profile. These data, comprising of body temperature, blood pressure, pulse oximetry and electrocardiogram, are throughput and transmitted over a wireless optical intra-cabin link to a server. Furthermore, and in order to reduce the cabin crew workload, along with the health data from a specific passenger group, seat-embedded safety sensors provide information for all passengers' flight safety parameters (such as table upright, seat-belt closed, etc.). The data gathered by the system in a central server can, in its entirety, be stored, processed or acted upon in real time.     

A Bioengineered In Vitro Model to Assess AAV-Based Gene Therapies for Cyclic GMP-Related Disorders

The emergence of efficient viral vectors derived from adeno-associated viruses (AAV) has led many groups to develop gene therapies for inherited monogenic diseases, such as retinal dystrophies. To evaluate the potency of new gene therapy vectors in a preclinical context, it is common to use animal models, such as gene-deficient or mutant animal models of a given human disease, and then assess vision restoration with functional or behavioral assays. While such animal models are invaluable to the preclinical testing process, they cannot be readily used as batch release tests during manufacturing or to validate biological activity at later stages of development. There is therefore a need for rapid and reliable in vitro models that can determine whether therapeutic vectors have delivered their cargo gene, and more importantly, whether this has resulted in the intended biological activity. Given our previous experience, we chose CNGA3-linked achromatopsia to develop a cell-based system to verify biological activity of AAV vectors designed to deliver a healthy CNGA3 gene copy into human cone photoreceptors. Our system is based on an immortalized cell line with high susceptibility to AAV transduction, i.e., HeLa cells, which we engineered to express a fungal rhodopsin guanylyl cyclase (RhGC) from Blastocladiella emersonii and a sensitive genetically encoded calcium indicator (GECI) under the control of a tetracycline operator. Using this system, we were able to confirm and quantify the function of the ion channel encoded by AAV/CNGA3 and differentiate between AAV vector potencies with a simple fluorometric assay. Finally, we show that this approach can be readily adapted for the assessment of phosphodiesterase function.     

Basic rate ISDN workstation traffic patterns

At present, the PC class of machine equipped with a modem and connected to the public switched telephone network (PSTN) finds many applications; access to electronic mail services, access to office computers by home-workers, occasional access to a mainframe from an isolated office, etc. Two developments are coinciding which will affect this usage; PCs are being upgraded into much more sophisticated workstations, and the PSTN is to be replaced by the integrated services digital network (ISDN), a digital service offering much greater bandwidth. These developments will have a significant effect on the ways in which isolated machines are used. Some results are presented from an assessment made at University College London on the extent to which modes of usage currently prevalent on LANs might translate to the ISDN workstation. Measurements have been made of traffic on a L LAN, and extrapolations have been made to gauge the effects of interposing ISDN both on performance and on cost.     

Oscillations of two competing microbial populations in configurations of two interconnected chemostats

It is known that, when two microbial populations competing for a single rate-limiting nutrient are grown in a spatially uniform environment, such as a single chemostat, with competition being the only interaction between them, they cannot coexist, but eventually one of the two populations prevails and the other becomes extinct. Spatial heterogeneity has been suggested as a means of obtaining coexistence of the two populations. A configuration of two interconnected chemostats is a simple model of a spatially heterogeneous environment. It has been shown that, when Monod's model is used for the specific growth rates of the two populations, steady-state coexistence can be obtained in such systems for wide ranges of operating conditions. In the present work, we study a model of microbial competition in configurations of interconnected chemostats and we show that, if a substrate inhibition model is used for the specific growth rates of the two populations, coexistence in a periodic state is also possible. The analysis of the model is done by numerical bifurcation theory methods.     

Use of natural clinoptilolite for the removal of lead, copper and zinc in fixed bed column

This work deals with the removal of lead, copper and zinc from aqueous solutions by using natural zeolite (clinoptilolite). Fixed bed experiments were performed, using three different volumetric flow rates of 5, 7 and 10bed volume/h, under a total normality of 0.01N, at initial pH of 4 and ambient temperature (25 degrees C). The removal efficiency increased when decreasing the flow rate and the following selectivity series was found: Pb(2+)>Zn(2+)> or =Cu(2+). Conductivity measurements showed that lead removal follows mainly ion exchange mechanism, while copper and zinc removal follows ion exchange and sorption mechanism as well.