The role of polymer (poly(vinylamine)) size (238-11000 units) on silicic acid condensation to yield soluble nanoparticles or composite precipitates has been explored by a combination of light scattering (static and dynamic), laser ablation combined with aerosol spectrometry, IR spectroscopy, and electron microscopy. Soluble nanoparticles or composite precipitates are formed according to the degree of polymerization of the organic polymer and pH. Nanoparticles prepared in the presence of the highest molecular weight polymers have core-shell like structures with dense silica cores. Composite particles formed in the presence of polymers with extent of polymerization below 1000 consist of associates of several polymer-silica nanoparticles. The mechanism of stabilization of the "soluble" silica particles in the tens of nanometer size range involves cooperative interactions with the polymer chains which varies according to chain length and pH. An example of the use of such polymer-poly(silicic acid) nanoparticles in the generation of composite polymeric materials is presented. The results obtained have relevance to the biomimetic design of new composite materials based on silica and polymers and to increasing our understanding of how silica may be manipulated (stored) in the biological environment prior to the formation of stable mineralized structures. We suspect that a similar method of storing silicic acid in an active state is used in silicifying organisms, at least in diatom algae.
This paper aims to analyze the mechanism of power absorption and to reveal, both experimentally and numerically, the basic factors determining the ability of plasma to absorb RF power. This is done by determining the plasma equivalent resistance value under different conditions in a low-pressure RF inductive discharge such as different antenna shape, working gas pressure, electron density, operating frequency and geometrical dimensions of the plasma source. Experimental and numerical results show that the plasma equivalent resistance changes non-monotonously with an increase in electron density, increases with an increase in neutral gas pressure, and that the maximum plasma equivalent resistance shifts toward higher electron densities when the operating frequency is increased.
At present, hemoglobin concentration and the volume of an erythrocyte can be determined from the intensities of light scattered by an individual cell at fixed angular intervals. This method is used in modern hemoglobin analyzers, but it requires calibration of optical and electronic units by certified particles of known size and refractive index. We describe a method that is based on the parametric solution of an inverse light-scattering problem and does not require a calibration procedure. The method is based on the use of parameters of the entire angular light-scattering pattern, called an indicatrix here. These parameters do not depend on the absolute intensity of light scattering. The indicatrix parameters form approximating equations that relate these parameters to the size and the phase-shift parameters of the particle. The applicability of the method is demonstrated by measurement of the indicatrices of individual sphered erythrocytes. The indicatrices of the individual erythrocytes were measured with a scanning flow cytometer at an angular range of from 15 to 55 deg. The volume and the hemoglobin concentration have been calculated by use of the developed method and by fitting of the experimental indicatrices to the indicatrices calculated from the Mie theory.
The present paper deals with the experimental and numerical study of radio-frequency (RF) lowpressure discharge having both inductive and capacitive or DC channels. Two discharge schemes are considered. In the first case the inductive and capacitive channels are powered by two independent RF power sources. In the second case the inductor and capacitor plates, being the main parts of inductive and capacitive channels, are connected in parallel to one RF power source. The properties of the mentioned discharges are compared with that of pure inductive RF discharge. It is shown that the presence of the capacitive component leads to changes of the fraction of RF power coupled through the inductive channel. This manifests with a reduction of the RF source power value, at which the transition from E-to H-mode takes place, and with the disappearance of hysteresis.
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