Silicone based surfactants were used as stabilizers for W/O/W double emulsions with unusual mech. stability. W/O/W multiple emulsions contg. several markers were prepd. The entrapped markers were: (1) halide salts, (2) a typical drug, ephedrine hydrochloride, and (3) KNO3 (water sol. fertilizer). Good solute trapping (95% yield of prepn.) with slow release rates through the liq. oil membrane (60% release after 30 days), were obtained. The halides, with the exception of iodide, showed almost the same typical slow release rates to the outer water phase. The release rates of the ephedrine hydrochloride and KNO3 were faster than that of the halides. The results suggested that multiple emulsions based on silicone surfactants can be used as slow release systems for agricultural applications. Up to 20 wt% of the total concn. of the hydrophobic silicone-based emulsifier (E1 - the inner emulsifier) was replaced by Span 80. As a result, water was entrapped in the oil phase, suggesting formation of reverse micelles in the presence of Span 80, explaining, in part, the release kinetics of the halides. The release seems to be composed of three sep. stages: lag time, fast release and "no release". The release mechanism seems to comply, in part, with a transport mechanism involving "reverse micelles" and is also dependent on the hydrophobicity of the marker. The more hydrophobic markers (the drug and iodide) seem to be released also by "direct diffusion of the mol. through the oil" in addn. to their release through the reverse micelles. [on SciFinder(R)]
Revised English version, "Carnival and Crisis in Three Stories by Nathaniel Hawthorne," in Towards the Ethics of Form in Fiction. Columbus: Ohio State University Press, 2010, pp. 21-34.
We must certainly give Gareth King the credit of putting the more informal varieties of the language on the map of linguistic description. However, when a work titled ‘Comprehensive Grammar’ professes on its first page the conviction that ‘… for the serious student of any language, grammar is a key to understanding and not an obstacle’ (vii), it is not over-rash to suspect the author has (or has had) some deep-lying misgivings about ‘grammar’. The book before us, I fear, amply confirms this inference.
Selective electrodes are electrochem. probes which are sensitive toward specific species. Most of these probes can be divided into two categories, i.e. potentiometric and voltammetric, based on the nature of the measurement. The major challenge is designing a selective electrode is introducing selectivity. The ultimate limit of their selectivity should make it possible to det. the levels of the analyte in unpolluted sea water. Through this manuscript two different approaches have been used as a means of developing voltammetric selective electrodes for heavy metals. The first concept involves the application of electrodes modified with crown ethers analogs. A selective electrode for gold ions was assembled by attaching an aza crown ether onto a glassy carbon surface. On the other hand an extremely sensitive electrode for mercury ions was developed based on a cryptand. Levels of mercury lower than 1 ppt could easily be detected using this probe. The electrode has been successfully applied for studying the release of mercury from dental amalgam. The second approach involves the formation of self-assembled monolayers with high affinity toward specific species. As an example, a selective electrode for cadmium ions is described. The electrode is made of ω-mercaptocarboxylic acid, HS(CH2)nCO2H, monolayers on mercury or gold surfaces. The detection limit of this electrode is 4 x 20̅12 M which is less than 1 ppt. The electrodes have been carefully studied and the parameters that govern their sensitivity as well as selectivity were optimized. Our major conclusion from this research is that very selective and sensitive probes can be developed by architecturing the solid-liq. interface at the mol. level. [on SciFinder(R)]
A computationally tractable approximation for both interstate and intrastate dynamics is derived and applied. The correlation between the electronic and nuclear degrees of freedom is explicitly allowed for in that there is an equation of motion for the nuclear dynamics on each electronic state. These equations for the intrastate dynamics are coupled due to the interstate interaction. The exact equations are derived from a quantum mechanical Hamiltonian and are then simplified by assuming that the coupling between the different electronic states is localized and that, in the absence of interstate coupling, the nuclear motion on each electronic state is classical-like. Equations for the populations and the phases of the different electronic states are also derived. Coupling of the nuclear modes to a classical solvent is included in the formalism and the main computational effort is in the mechanical description of the solvent. As a computational example, a simulation of a fast pump-fast probe for an iodine X –> B (bound) transition, in rare gas solvents, is presented and discussed. Despite the long range of the B state potential of iodine, which enhances the effect of the solvent on the excited state dynamics, there is a finite delay before the coupling to the solvent is manifested. The delocalization of the optically prepared state markedly slows down as the density is lowered. At longer times there is considerable energy exchange with the solvent. As a result many molecules either gain enough energy to dissociate or are cooled down, depending on the temperature and density of the solvent. At the higher densities, many molecules which attempt to dissociate are caged.
The conjunctive is still the most mystifying clause-form in Egyptian, from LE through Demotic to Coptic. For several reasons, including its shadowy origins and puzzling morphology, but especially because of its elusive semantics and syntactic properties, and indeed, its syntactic essentials, it is still not clearly understood and probably often misinterpreted. […]
The elastic behavior of mixed bilayers composed of two amphiphilic components with different chain length (and identical head groups) is studied using two molecular level models. In both, the bilayer free energy is expressed as a sum of chain, head group and interfacial contributions as well as a mixing entropy term. The head group and interfacial terms are modeled using simple phenomenological but general expressions. The models differ in their treatment of the chain conformational free energy. In one it is calculated using a detailed mean-field molecular theory. The other is based on a simple `'compression'' model. Both models lead to similar conclusions. Expressing the bilayer free energy as a sum of its two monolayer contributions, a thermodynamic stability analysis is performed to examine the possibility of spontaneous vesicle formation. To this end, we expand the bilayer free energy as a power series (up to second order) in terms of the monolayer curvatures, their amphiphilic compositions and the average cross sectional areas per molecule; all variables are coupled, with the molecular composition and areas treated as degrees of freedom which are allowed to relax during bending. Using reasonable molecular interaction parameters we find that a second order transition from a planar to a curved (vesicle) geometry in a randomly mixed bilayer is unlikely. Most of our analysis is devoted to calculating the spontaneous curvature and the bending rigidity of the bilayer as a function of its amphiphile chain composition. We find that adding short chain amphiphiles to a layer of long chain molecules reduces considerably its bending rigidity, as already known from calculations involving only the chain contributions. However, we find that inclusion of head group and interfacial interactions moderates the effect of the added short chains. We also find that the bending rigidity Of pure monolayers is approximately linear in chain length, as compared to the nearly cubic dependence implied by the chain free energy alone (at constant head group area). Our main result involves the calculation of the spontaneous curvature as a function of composition. We find, for different chain mixtures, that upon adding short chains to long chain monolayers, the spontaneous curvature first increases nearly Linearly with composition and then (beyond mole fraction of about 0.5) begins to saturate towards the spontaneous curvature of a pure short chain layer. Qualitative arguments are provided to explain this behavior. (C) 1995 American Institute of physics.
This article is the first in a series of corpus-based profiles or sketches of certain central subsystems of Mabinogi Middle Welsh grammar. These aim at putting pattern-sets, patterns and pattern details in their proper perspectives of values, relevancies and relationship network, by applying structural-analytic procedure to complex phenomena of synax hitherto not treated systematically in this approach. viz. in terms of oppositions and neutralizations, of paradigmatic (categorial constituency) and syntagmatic (compatibility) properties, commutabilities and compatiblities.
The etching of silicon has been studied by the scanning electrochem. microscope (SECM) technique. Etching has been accomplished in acidic fluoride solns. by electrogenerating a strong oxidant, i.e. bromine in this case, at an ultramicroelectrode which was held closely above a silicon 〈111〉 wafer. The parameters that affect the process and control the efficiency of the silicon etching were examd. A detailed mechanism of the process, which was derived from the unique advantages of the SECM and is in agreement with previous reports, is proposed. [on SciFinder(R)]
The time-dependent self-consistent field (TDSCF) approximation is applied to the coupled-mode vibrational dynamics of highly anharmonic quantum clusters, and its validity and accuracy for such systems are tested against exact quantum calculations. The calculations are pursued for bound but non-stationary states of collinear models of (Ne)(3) and B(H-2)(2). It is found that for a short timescale (t less than or equal to 1 ps) the TDSCF approximation is in excellent accord with the exact results. This suggests that TDSCF should be an attractive quantitative approach for the short timescale vibrational dynamics of highly anharmonic quantum clusters.
A molecular model is used to calculate the free energy of mixed vesicles and cylindrical micelles, composed of lipid molecules and short chain surfactants. The free energy of both aggregates (modeled as an infinite planar bilayer and an infinite cylindrical aggregate) is represented as a sum of internal free energy and mixing entropy contributions. The internal free energy is treated as a sum of chain (conformational), head group, and surface tension terms. Calculating the free energy of each aggregation geometry as a function of lipid/surfactant composition and using common tangent construction we obtain the compositions of the bilayer and the micelle at the phase transition. By varying certain molecular parameters (such as the `'hard core'' area of the surfactant head group or the length of the surfactant tail) we study the role of molecular packing characteristics in determining the compositions at phase coexistence. We find, as expected, that upon increasing the preference of the surfactant for the micellar geometry (larger spontaneous curvature) the bilayer is solubilized at lower surfactant/lipid concentration ratios. For some typical values of the parameters used, reasonable agreement with experimental results for mixtures of egg phosphatidylcholine and octylglucoside is obtained.
