PubMed · 13913294
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L SINGER, W D ARMSTRONG. Modified diffusion method for analysis of fluoride.. https://doi.org/10.1177/00220345620410042601
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A novel diffused photon-pair density wave (DPPDW) composed of correlated polarized photon pairs at different temporal frequencies and orthogonal linearly polarized states is proposed. A theory of DPPDWs is developed. A DPPDW selected by coherence gating and polarization gating that satisfies the diffusion equation has been verified experimentally. The sensitivity of amplitude and phase detection of the heterodyne signal has been improved by the properties of synchronized detection and common-path propagation of polarized pair photons in a multiple-scattering medium. Both reduced scattering coefficient micro2s' and absorption coefficient micro2alpha of the scattering medium in terms of the measured phase and amplitude of the heterodyne signal have been obtained. The detection sensitivity of micro2s' and micro2alpha and the properties of a DPPDW in a multiple-scattering medium are discussed and analyzed.
The drying of hydrogel films formed by poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers (Pluronic P105 and Pluronic L64) is investigated at various air relative humidity (RH) conditions in the range 11-94%. These amphiphilic block copolymers self-assemble to form a variety of ordered (lyotropic liquid crystalline) structures as the water content decreases. The amount of water lost increases linearly with the drying time initially (constant rate region, stage I). After this linear region, a falling rate is observed (stage II). The drying rate increases with decreasing RH, thus greatly shortening the drying time. A decrease of the initial film thickness or a decrease in the initial water content shortens the drying time; however, the drying mechanism remains the same. Analysis of the experimental data shows that the hydration level in the Pluronic hydrogel mainly determines the drying rate, rather than the type of ordered structure formed. Two distinct regions (liquid/gel and solid/crystalline) are observed in the drying isotherm for PEO-PPO block copolymers and homopolymer poly(ethylene glycol)s. A model for one-dimensional water diffusion is used to fit the experimental drying results at different RH, initial film thickness, and initial water content conditions. The model accounts for the shrinkage of the film during drying and for a water diffusion coefficient that is a function of the water concentration in the film. For the experimental conditions considered here, the Biot number (Bi) is less than unity and the drying is mainly limited by evaporation at the film surface. The diffusion model is used to obtain information for cases where Bi > 1.
We investigate the effect of time-dependent noise on the shape of a morphogen gradient in a developing embryo. Perturbation theory is used to calculate the deviations from deterministic behavior in a simple reaction-diffusion model of robust gradient formation, and the results are confirmed by numerical simulation. It is shown that such deviations can disrupt robustness for sufficiently high noise levels, and the implications of these findings for more complex models of gradient-shaping pathways are discussed.