Determination of Particle Size Distribution by Laser Diffraction of Doped‐CeO2 Powder Suspensions: Effect of Suspension Stability and Sonication

The particle size distributions (PSDs) of metal oxide powders are often determined by analyzing suspensions of powders using laser diffraction (e.g. Malvern MasterSizer 2000). Particle agglomeration can effectively bias the resulting distribution towards “unrealistic” particle sizes. Solutions to avoid this problem must be found if a particle distribution based on the elemental or primary particle sizes is desired. In this work, the particle size distribution of doped‐CeO₂ powders was studied. These powders show a crystalline single phase structure of controlled stoichiometry as determined by X‐ray diffraction and ICP analysis. The apparent size distribution was found to be a strong function of suspension stability. Dispersant agents (PBTCA and phosphonoacetic acid) and suspension pH affected stability as characterized by zeta potential measurements. Sonication of the suspensions further enhanced particle de‐agglomeration. Finally, only the combined effect of a dispersant agent, pH adjustment of the suspension and sonication provided a primary particle size distribution. The results presented in this work can be used in the analysis of similar ceramic powders in which strong particle agglomeration is present.     

Exact periodic solutions and chaos in the semiclassical Jaynes-Cummings model

Exact periodic solutions for the semiclassical Jaynes-Cummings model without the assumption of the rotating-wave approximation are studied. They are valid for some specific values of the coupling constant, detuning parameter and the energy of the system. The behaviour of the system in the vicinity of this special solution is studied numerically. By computation of the Fourier spectrum, it is shown that the behaviour of the system changes from a non-chaotic to a chaotic one when the energy of the system increases.     

Vocal Tremor Reduction with Deep Brain Stimulation: A Preliminary Report

Vocal tremor has been a challenging problem for patients and their physicians. In some cases, it has been possible to lesson the symptom's tremor through medications and/or voice therapy. However, in most cases no good treatment has been available. Chronic stimulation of the thalamus has been successful in controlling tremors of the upper limb and other portions of the body. Our preliminary experience suggests that it may also be helpful in controlling vocal tremor.     

Determination of basic drugs of abuse in human serum by online extraction and LC–MS/MS

A new quantitation method for the determination of drugs of abuse (opiates, amphetamine and derivatives, cocaine, methadone and metabolites) in serum by using online extraction coupled to liquid chromatography (LC)–mass spectrometry (MS)/MS has been developed. The online extraction is carried out using two extraction columns simultaneously and one analytical column. One extraction column is loaded, while the other one is eluted by a gradient. The elution gradient also separates the analytes in the analytical column. For the sample preparation, serum is spiked with a mixture of deuterated analogues of the drugs. After protein precipitation with methanol/zinc sulphate, centrifugation, evaporation and reconstitution, the sample is injected into the LC system. The quantitation is based on the analysis of two multiple reaction monitoring transitions per drug. The recovery of the protein precipitation step is over 80% for all analytes. Intra- and interday precision, as relative standard deviation, is lower than 6%, and in the case of accuracy, RE is lower than 15%. Only the most polar analytes showed matrix effects. The limits of quantitation for the analysed compounds vary between 0.5 and 2.8 ng/mL. The developed method was used to quantify basic drugs in samples “from driving under the influence of drugs” cases. The results were compared with those obtained by using solid-phase extraction–GC–MS.     

Chaotic behavior in quantum optics and the failure of the Rotating-Wave Approximation at high intensities

We consider the semiclassical theory of a collection of two level atoms interacting with a single mode electric field. In this model the in quantum optics usually applied RWA fails at high field intensities. It is shown that the theory without applying the RWA can lead to a chaotic behavior, which can be described by a parametrically forced pendulum equation. The dynamics become more and more complicated if the electric field is increased. For extremely high intensities we obtain again a regular behavior described by a pendulum equation with a modified potential. In this case the dynamics is greatly different from the results obtained within RWA.     

Rabi-oscillations without rotating-wave approximation

We consider the interaction of an ensemble of two level atoms with linearly polarized light. This problem is solved in terms of the well-known Bloch equations for various amplitudes of the incident light field without rotating-wave approximation (RWA). Closed-form solutions are obtained for small and very high electric field amplitudes. In the latter case severe deviations from the results obtained with RWA are observed.     

Optimization of dye-laser output coupling by consideration of the spatial gain distribution

The problem of output-coupling optimization of a transversely or longitudinally pumped dye laser is treated in terms of a rate equation approach under steady state considerations. The theoretical study considers the spatial variation of the gain distribution and such typical features of a dye laser as reabsorption, triplet effects and excited state absorption. Numerical results obtained with realistic values of typical laser parameters (cross-sections for stimulated emission and reabsorption, number density of active molecules etc.) indicate that a higher degree of output coupling and consequently higher output powers are feasible upon a complete consideration of the spatial gain distribution     

Stiffness variation in the interphase of amine‐cured epoxy adjacent to copper microstructures

In an effort to expand the understanding of the mechanical properties of the polymeric interphase on a metal surface, a composite consisting of epoxy and copper was prepared and analyzed. Scanning force microscopy‐based force modulation microscopy (SFM‐FMM) was employed along with dynamic mechanical analysis (DMA) and energy dispersive X‐ray analysis (EDX). Diglycidyl ether of bisphenol A (DGEBA)‐based epoxy resins were applied with amine curing agents. The samples were made taking advantage of electron beam lithography (EBL) in order to produce sharp edges of copper structures and a flat surface suitable for the SFM‐FMM analysis, which was able to depict the stiffness within the interphase. It is considered significant information because the mechanical characteristic within the narrow interphase was revealed. Comparing with DMA and EDX, the stiffness information of SFM‐FMM demonstrated a matching correlation and agreement in terms of preferential adsorption of the curing agent in the vicinity of the interface. The stiffness profiles of the two epoxy systems turned out to be different, and it shows the material dependence of the interphase characteristics. Copyright © 2007 John Wiley & Sons, Ltd.