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Southwell's analysis of optical multilayers within the limits of very thin films has been extended to include absorption in the multilayer for predicting the effective values of the refractive index [n.sub.e] and extinction coefficient [k.sub.e] of mixed-composition binary homogeneous films over a wide spectral region, including the high-absorption (k > [10.sup.-2]) region. It has been found that [n.sub.e] in general is a complicated function of the optical parameters ([n.sub.1], [k.sub.1], [n.sub.2], [k.sub.2]) and volume fractions ([f.sub.1], [f.sub.2]) of the component materials in a homogeneous layer, and the expression for [n.sub.e] becomes the same as that predicted by the Drude model in the spectral region where the layers are transparent. Moreover, according to the present analysis, the volume fractions of the product of the refractive index and the extinction coefficient of the component materials of a binary composite film are additive and the sum equals the product of the effective refractive index and extinction coefficient of the composite film. OCIS codes: 300.1030, 230.4170.

Abstract Background SPARC is a matricellular protein involved in cell-matrix interactions. From expression patterns at the wound site and in vitro studies, SPARC has been implicated in the control of wound healing. Here we examined the function of SPARC in cutaneous wound healing using SPARC-null mice and dermal fibroblasts derived from them. Results In large (25 mm) wounds, SPARC-null mice showed a significant delay in healing as compared to wild-type mice (31 days versus 24 days). Granulation tissue formation and extracellular matrix protein production were delayed in small 6 mm SPARC-null wounds initially but were resolved by day 6. In in vitro wound-healing assays, while wild-type primary dermal fibroblasts showed essentially complete wound closure at 11 hours, wound closure of SPARC-null cells was incomplete even at 31 hours. Addition of purified SPARC restored the normal time course of wound closure. Treatment of SPARC-null cells with mitomycin C to analyze cell migration without cell proliferation showed that wound repair remained incomplete after 31 hours. Cell proliferation as measured by 3H-thymidine incorporation and collagen gel contraction by SPARC-null cells were not compromised. Conclusions A significant delay in healing large excisional wounds and setback in granulation tissue formation and extracellular matrix protein production in small wounds establish that SPARC is required for granulation tissue formation during normal repair of skin wounds in mice. A defect in wound closure in vitro indicates that SPARC regulates cell migration. We conclude that SPARC plays a role in wound repair by promoting fibroblast migration and thus granulation tissue formation.

Lithium silicate (LS) ceramics were prepared via a solid-state reaction technique. Two ceramics with different molar ratios of LiCO/SiO (1:1 and 1:2) were prepared for dielectric studies. X-ray diffraction pattern showed that LiCO/SiO (1:1) ceramic is obtained as single phase composition whereas LiCO/SiO (1:2) ceramic exhibit a multiphase structure with LiSiO as a major phase. Microstructural analysis shows that the compounds have well defined grains separated by grain boundaries. Dielectric and electrical properties of the samples were studied in a wide temperature (30-400 °C) and frequency ranges (100 Hz-5 MHz). From the dielectric studies, we can prescribe LiCO/SiO (1:2) ceramic as a good dielectric material since it possesses low dielectric loss. Detailed analysis of the impedance data suggests that the conduction of LiCO/SiO (1:2) ceramic is mainly due to the bulk effects whereas the complex impedance plots of LiCO/SiO (1:1) ceramic suggests the presence of both bulk as well as grain boundary contributions. The bulk resistance of the samples has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance behavior. The low activation energies of the samples suggest the presence of singly ionized oxygen vacancies in the conduction process. [ABSTRACT FROM AUTHOR]

Lithium metasilicate (Li2SiO3) ceramic was prepared via solid-state reaction technique. The formation of the compound in an orthorhombic crystal structure was confirmed by an X-ray diffraction (XRD) technique. Surface morphology of the compound was studied by field emission scanning electron microscopy (FE-SEM). Detailed studies on the electrical behavior (complex impedance [Z*], electrical conductivity and relaxation mechanism) of the Li2SiO3 ceramic have been carried out at various temperatures. The Nyquist plots suggest that the grains and grain boundaries are responsible in the conduction mechanism of the material at high temperature. The frequency dependent conductivity and dielectric relaxation of Li2SiO3 ceramic are investigated over a frequency range from 100 Hz to 5 MHz and in a temperature range from 35 °C to 350 °C by using alternating current impedance spectroscopy. The conductivity isotherms show a transition from frequency independent dc region to dispersive region where the conductivity continuously increases with the increasing frequencies. [ABSTRACT FROM AUTHOR]