Synthesis and biological evaluation of 4-chloro-3, 5-dinitrobenzotrifluoride analogues as antileishmanial agents

Desnitro analogues of 4-chloro-3,5-dinitrobenzotrifluoride (chloralin) (2), an in vitro microtubule inhibitor of several Leishmania species, have been synthesized from 2-halo-5-(trifluoromethyl)benzenesulfonyl chlorides 4 and 5. The analogues exhibited moderate to excellent activity when tested against Leishmania donovani amastigotes in vitro. Two representative compounds, 7f and 8, were tested against the Khartoum strain of L. donovani in a hamster model using chloralin (2) and Glucantime (one of the current therapeutics of choice in the treatment of Leishmania) as standards, the results of which will be discussed herein.     

Polymerisation reactions initiated by high electric fields. Kinetic applications in the field of free cationic polymerisations

Free cationic polymerisations were initiated in bulk by field ionisation with a positive tip. Dilatometric measurements obtained with ‘dry’ and ‘ultra-dry’ styrene, a-methylstyrene and isobutylvinylether were in agreement with kinetic equations derived by assuming that in the absence of deactivating impurities the space charge is built up only by growing macromolecules. Determination of the space charge by independent physical methods suggests that the k_p values of the literature need to be re-evaluated. It was also shown that charge injection enhances the degree of dryness (measurable by this process) and is therefore useful in ultimate purification of monomers.     

Frictional properties of solid lubricants modified by polymer grafting

The surface of finely divided solid lubricants such as MoS₂, (CF_x)_n and graphite is modified by grafting of different polymers. Study of the tribological properties of the grafted products under conditions of dry sliding showed that the coefficient of friction, as well as surface properties such as film formation and adhesion, are improved. The effect is especially marked with grafted MoS₂ and depends on the nature and chemical stability of the grafted polymer. The apparent joint effect of easier plastic deformation suggests that this may be related to a Rehbinder effect (superficial plasticization of the metal). With MoS₂ and (CF_x)_n suspended in paraffin oil, grafting improves the load-carrying capacity.     

Plasma treatment effect on the surface energy of carbon and carbon fibers

The surface energy dispersive (γ^D_S) and polar (γ^P_S) components of carbon model surfaces (bal planes, prismatic surfaces, vitreous carbon) and of carbon fibers (high strength and high modulus, respectively) were determined systematically before and after plasma treatment. The method used is essentially based on the wetting contact angle measurements within two liquids. In all cases (γ^P_S) is markedly increased by the plasma treatment. For carbon fibers, with increasing plasma treatment duration (γ^P_S) is increasing toward a limiting value (-30 mJ/m²) while (γ^D_S) is depressed toward low values (-10 mJ/m²). The parallel evolution of surface topography is followed by SEM observations. The changes in surface energy of carbon model surfaces is also discussed.     

A computer-controlled eight-channel pulse generator

An eight-channel pulse generator able to generate signal transitions synchronized to an internal 10-MHz clock or an external clock is described. The time intervals between transitions can be programmed arbitrarily with a time resolution of one clock period. The generator is realized as a PC add-in board.     

Dynamic sorption of ionizable organic compounds (IOCs) and xylene from water using geomaterial-modified montmorillonite

Adsorption of phenols and xylene onto composite material, Na-montmorillonite, activated carbon, cement and water mixture, 70%, 7%, 7% and 16% (w/w/w/w), respectively, was studied at pH values of 5.15, 4.55, 5.2 and 4.9, respectively, of phenol, 2-CP, 2-NP and xylene. Equilibrium isotherms and fixed-bed column studies were undertaken to evaluate the performance of clay-active coal-coated cement (CACC) in removing phenols from aqueous solution. Investigations revealed CACC to be a very efficient media for the removal of phenols from water. The suitability of the Langmuir adsorption model to the equilibrium data was investigated for all phenols-adsorbent systems. At the maximum sorption capacity of the composite material it was found that the uptake (mg phenols/g) of phenols increased in the order 2-CP>2-NP>phenol approximately m-xylene as do their solubilities. The LUB design approach was used to determine the equivalent length of unused bed. The lower LUB values imply a better utilization of CACC composite. A model, which considered the effect of axial dispersion, was successfully used to describe the fixed-bed operation, the axial dispersion coefficient increased significantly with solubility.     

All in good time: knowledge introduction,restructuring, and development of shared opinions as different stages in collaborative writing

When learners collaborate with each other in order to elaborate on a particular subject, this collaboration may be influenced by the differing perspectives the learners have on the topic. There has been very little research to date on how differing perspectives have an impact in collaboration situations in which people are supposed to form a shared opinion on a particular topic. In this study, we analyzed which stages people’s activities pass through on their way to reaching shared opinions in a collaborative writing task. We examined how dyads of secondary school students, who in a previous instructional session had dealt with differing theoretical approaches to media effects, collaborated in writing a shared text about the topic of media violence. Quantitative analysis indicated that the participants engaged in different activities at different stages of the collaboration processes: In the early stages they were predominantly engaged in introducing the knowledge that they had acquired in the previous lesson. This activity was replaced in the middle stage of the collaboration by restructuring activities. Forming and phrasing shared opinions rarely occurred until very late in the collaboration, but played the leading role in the final stage. We applied a qualitative content analysis to illustrate these different activities by presenting examples of the collaboratively written texts. In doing so, we discuss the distinct activities as well as their character and functionalities for collaboration.     

Upgrade of coaxial CATV networks for upstream high speed digitalcommunication

There is a growing interest to extend existing coax CATV networks to enable interactive multimedia services. In this paper we describe necessary modifications and additions of CATV network components to provide broadband upstream channels in the range of 6 to 40 MHz. To investigate linear and nonlinear distortions, reflexions, noise and ingress, suitable digital modulation schemes and adaptive equalization, the CATV network-components are modelled and a computer simulation program using PTOLEMY is established. It is shown that all 3370 subscribers of an existing CATV sub-network can be provided with up to 25 kbit/s collision free on the physical network layer. Using appropriate teletraffic and media access control protocols, user bit rates of up to 2 Mbit/s are feasible in the upstream direction     

20·5% efficient silicon solar cell with a low temperature rear side process using laser‐fired contacts

The paper presents a rear side structure for crystalline silicon solar cells, which is processed at a maximum temperature of 220°C. Using two different material compositions for electrical and optical needs, the layer system has excellent passivation properties, enhances light trapping and allows for a good ohmic contact. With this structure we achieve an independently confirmed conversion efficiency η=20·5% on a 250 μm thick silicon solar cell. Due to the fact that the maximum process temperature is 220°C, this layer system enables new solar cell concepts. Copyright © 2006 John Wiley & Sons, Ltd.     

150-mm layer transfer for monocrystalline silicon solar cells

We report on recent improvements concerning the transfer of monocrystalline silicon layers to plastic substrates for flexible solar cell applications. Finite element numerical modeling of the etching current density distribution allows for optimizing our electrochemical etching setup for separation layer formation. By modifying the setup according to the simulation results, we are now able to transfer 25 μm thick monocrystalline silicon sheets with up to 150 mm in diameter.