Abbass Hashim

Optical detection of microcystin produced by cyanobacteria

Microcystin (MC-LR) produced by cyanobacteria (blue-green algae) was detected in direct immunoassay with specific monoclonal antibody MC10E7 using an optical method of Total Internal Reflection Ellipsometry (TIRE). The minimal detected concentration of MC-LR of 0.1 ng/ml is a remarkable achievement for direct immunoassay against such low molecular weight analyte molecule. The study of binding kinetics of MC-LR to MC10E7 antibody allowed the evaluation of the association constant KA of about 108 (l/Mol) typical for highly specific immune reactions. Concentration of MC-LR in aqueous solutions was reduced using an absorbent made of polyelectrolyte-coated microparticles functionalized with MC10E7 antibodies.

Formation of an interface layer in thermionic oxide cathodes for CRT applications

Scanning electron microscopic techniques were employed to study the surface morphological changes of oxide cathodes and nickel caps as a result of cathode activation extending over periods of 1?12?h. Elemental analysis of barium, strontium, tungsten, magnesium and aluminium was performed using energy dispersion x-ray spectroscopy. An abrupt change was observed after activation longer than 3?h. Conduction through well activated cathode assemblies was found to be due to intergranular electron tunnelling at low temperatures (T ? 500?K), while trapping and detrapping at grain boundaries becomes the dominant mechanism at high temperatures (T ? 500?K). The contribution of the interfacial layer to conductivity was found to be significant for cathodes activated for smaller periods.

Activation process-dependent characteristics of novel thermionic oxide cathodes for CRT application

The emission and conductivity characteristics of oxide cathodes depend largely on the activation process. In this paper, the electrical properties of new type of oxide cathodes for cathode ray tube (CRT) application, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes. The influence of the activation process over different durations has been investigated. A temperature of T=1425 K was chosen to be higher than the optimum cathode activation temperature (T=1200 K), and the other temperature of T=1125 K was lower than that. The electron activation energy (E) was found to vary in the range from 0.58 to 2.28 eV for cathodes activated at the higher temperature regime, and from 1.08 to 1.9 eV for those activated at the lower temperature regime. Scanning electron microscopy (SEM) and electron diffraction X-ray (EDX) analyses show a structural phase transformation in the oxide material that was activated at 1125 K for a period of 1-12 hours. The SEM mapping shows a large contamination of Ba in the top layer of oxide material. The activator agents tungsten and aluminum are found to penetrate into the BaO/spl bsol/SrO layer in two different ways.

Effects of activation time and temperature on electrical conductivity of novel cermet oxide cathodes for CRT applications

A new generation of oxide cermet cathodes was activated at 850 and 1150 °C for various lengths of time. The grain boundaries in the oxide layer increased with activation time for the cathodes activated at 850 °C. The growth of interfacial Al2O3 and WO3 layers and the concentration of free Ba on the surface for activation at 850 °C for a period less than 3 h were found to be different from the ones observed for longer than 3 h. This type of behaviour was not observed for the cathodes at 1150 °C. The conductivity measured at low temperatures on a cathode activated at 850 °C was much higher for long activation than for a short period of activation. Activation at 1150 °C for a period longer than 2 h produced a disruptive effect of low conductivity and high activation energy.

Detection of γ-radiation and heavy metals using electrochemical bacterial-based sensor

The main aim of this work is to develop a simple electrochemical sensor for detection of γ-radiation and heavy metals using bacteria. A series of DC and AC electrical measurements were carried out on samples of two types of bacteria, namely Escherichia coli and Deinococcus radiodurans. As a first step, a correlation between DC and AC electrical conductivity and bacteria concentration in solution was established. The study of the effect of γ-radiation and heavy metal ions (Cd2+) on DC and AC electrical characteristics of bacteria revealed a possibility of pattern recognition of the above inhibition factors.

Resistivity network and structural model of the oxide cathode for CRT application

In this paper, the electrical properties of oxide cathode and oxide cathode plus, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes and methods. Oxide cathode activation treatment for different durations has been investigated. The formations of the compounds associated to the diffusion of reducing elements (Mg, Al, and W) to the Ni cap surface of oxide cathode were studied by a new suggestion method. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) was used as analytical techniques. Al, W, and Mg doping elements take place during heating to 1080 K (Ni-Brightness) under a rich controlled Ba-SrO atmosphere through an acceleration life test. The chemical transport of these elements was occurred mainly by the Ni cap grain boundary mechanism with significant pile-up of Mg compounds. Al and W show a superficial concentrations and distribution. A new structural and resistivity network model of oxide cathode plus are suggested. The new structural model shows a number of metallic and metallic oxide pathways are exist at the interface or extended through the oxide coating. The effective values of the resistances and the type of the equivalent circuit in the resistivity network model are temperature and activation time dependent

The effect of the high and low activation temperature on the conduction of thermionic oxide cathodes for CRT applications

The influence of the activation time and temperature on electrical properties of a new type of cathodes was investigated. Electrical results were interpreted in terms of the changes in the surface morphology and composition consequent upon the activation process.