Calculation of emittance of a disperse system

The emittance of a disperse system is calculated under the assumption that the particles forming the system have a diffuse gray surface. The calculated results are compared with experiment.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 6, pp. 983–988, June, 1980.     

Revised Kubelka-Munk theory. I. Theory and application

Using a statistical analysis of light propagation in media, we propose a revision to Kubelka-Munk (K-M) theory by taking into account the effect of scattering on the path length of light propagation (path variation). This leads to new relationships between the K-M scattering S and absorbing K coefficients and the intrinsic scattering s and absorbing a coefficients of a material that indicate that the S and K coefficients depend non-linearly on both a and s. The additivity law that bridges K-M S and K coefficients of a composite medium, such as dye-dispersed paper (dyed paper) and those of its material components (dye and paper), is also revised. It is further shown that experimental findings on dyed paper that the original K-M theory failed to explain can be clearly understood and accommodated by the new K-M theoretical framework (two-flux approach). Numerical simulations with the revised theory on model ink, paper, and dyed paper have been carried out.     

Examination of the revised Kubelka-Munk theory: considerations of modeling strategies

The revised Kubelka-Munk theory is examined theoretically and experimentally. Systems of dyed paper sheets are simulated, and the results are compared with other models. The results show that the revised Kubelka-Munk model yields significant errors in predicted dye-paper mixture reflectances, and is not self-consistent. The absorption is noticeably overestimated. Theoretical arguments show that properties in the revised Kubelka-Munk theory are inadequately derived. The main conclusion is that the revised Kubelka-Munk theory is wrong in the inclusion of the so-called scattering-induced-path-variation factor. Consequently, the theory should not be used for light scattering calculations. Instead, the original Kubelka-Munk theory should be used where its accuracy is sufficient, and a radiative transfer tool of higher resolution should be used where higher accuracy is needed.     

Computational analysis of thin coating layer failure using a cohesive model and gradient plasticity

Thermal barrier coatings (TBC) are widely used to prevent transient high temperature attack and allow components high durability. Due to strong inhomogeneous material properties the TBC failure often initiates near the interface between the brittle oxide layer and the ductile substrate. A reliable prediction of the TBC failure requires detailed information about the crack tip field and the consequent fracture criteria. In the present paper both cohesive model and gradient plasticity are used to simulate the failure process and to study interdependence of the interface stress distribution with the specific fracture energies. Computations confirm that combination of the two models is able to simulate different failure mechanisms in the TBC system. The computational model has the potential to give a realistic prediction of the crack propagation process.     

铜热浸镀铝扩散层生长动力学模型

采用一浴法对铜进行了热浸镀铝试验,热浸镀时间为10~25s,热浸镀温度为963~1 013K。研究了热浸镀温度和时间对铜铝复合材料界面扩散层厚度的影响,采用XPL-15型偏光显微镜(PM)测量铜铝复合材料扩散层厚度,并依据热浸镀铝试验建立了铜铝复合材料界面扩散层生长动力学模型。结果表明,铜铝复合材料界面扩散层的生长动力学符合抛物线扩散规律,与热浸镀温度的指数成正比,与热浸镀时间成抛物线增长关系;铜热浸镀铝扩散层生长动力学模型的修正系数k与时间t存在线性关系。     

Characterization of sputtered triple layer photoactive coating with a glass-like appearance

Photocatalytic activity of sputtered TiO₂ single layer was investigated. From the results on the optical constants analyses and dark- and photo-conductivity measurements, it is revealed that the photocatalytic activities of TiO₂ films depend on the defect density of the TiO₂ films; the atomic defects act as recombination sites for photo-generated carriers diffusing to the TiO₂ surface. A three-layer system with a layer construction of SnO₂/TiO₂/Si₃N₄/Glass was designed for realizing the glass-like appearance, namely almost the same transmission and reflection spectra in visible wavelength region as those of glass, and its photocatalytic activity was investigated. The experimental results indicate that the interface between TiO₂ and SnO₂ acts as a potential barrier for the carriers photo-generated in the TiO₂ and the photo-generated species pass through the SnO₂ overlayer depending on the SnO₂ film characteristics.     

Novel fabrication of a polymer scaffold with a dense bioactive ceramic coating layer

A novel method of coating a polymeric scaffold with a dense ceramic layer was developed. This method exploits the fact that only one of the two interlaced 3-D channels formed in a ceramic dual-scaffold can be infiltrated with a polymer. Firstly, a 3-D graphite network prepared by the rapid prototyping (RP) method was dip-coated with hydroxyapatite (HA) slurry, followed by heat-treatment at 1250°C for 3 h in air. This created an additional 3-D channel through the removal of the graphite network, while preserving the pre-existing 3-D channel. Thereafter, only one channel was infiltrated with a molten poly(ε-caprolactone) (PCL) polymer at 140°C for 12 h, producing a PCL scaffold with a dense, uniform HA coating layer. The sample showed high compressive strength with ductile behavior, due to the nature of the PCL polymer, and an excellent cellular response afforded by the bioactive HA coating layer. The results indicate that this novel technique provides a highly versatile method of coating various polymeric scaffolds with bioactive layers in order to endow them with advanced functionalities.     

High-performance triisopropylsilylethynyl pentacene transistors via spin coating with a crystallization-assisting layer

The effects of spin speed and an amorphous fluoropolymer (CYTOP)-patterned substrate on the crystalline structures and device performance of triisopropylsilylethynyl pentacene (TIPS-PEN) organic field-effect transistors (OFETs) were investigated. The crystallinity of the TIPS-PEN film was enhanced by decreasing the spin speed, because slow evaporation of the solvent provided a sufficient time for the formation of thermodynamically stable crystalline structures. In addition, the adoption of a CYTOP-patterned substrate induced the three-dimensional (3D) growth of the TIPS-PEN crystals, because the patterned substrate confined the TIPS-PEN molecules and allowed sufficient time for the self-organization of TIPS-PEN. TIPS-PEN OFETs fabricated at a spin speed of 300 rpm with a CYTOP-patterned substrate showed a field-effect mobility of 0.131 cm(2) V(-1) s(-1), which is a remarkable improvement over previous spin-coated TIPS-PEN OFETs.     

Revised Kubelka-Munk theory. III. A general theory of light propagation in scattering and absorptive media

A generally applicable theoretical model describing light propagating through turbid media is proposed. The theory is a generalization of the revised Kubelka-Munk theory, extending its applicability to accommodate a wider range of absorption influences. A general expression for a factor taking into account the effect of scattering on the total photon path traversed in a turbid medium is derived. The extended model is applied to systems of ink-dyed paper sheets-mixtures of wood fibers with dyes-which represent examples of systems that have thus far eluded the original Kubelka-Munk model. The results of simulations of the spectral dependence of Kubelka-Munk coefficients of absorption and scattering show that they compare very well with those derived from experimental results.     

Calculation of the incompressible laminar boundary layer on a plate with slot suction

The dependence of the characteristics of an incompressible laminar boundary layer on the flow rate of fluid removed by suction through transverse slots on the surface of a plate is investigated on the basis of the momentum equation.     

One approach to calculating a turbulent boundary layer on a surface with a compliant coating

A method is proposed for calculating a turbulent boundary layer on a surface with a viscoelastic coating. The method is based on the introduction of the van Driest damping function to account for the effect of the coating on the boundary layer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 4, pp. 657–663, April, 1981.     

Barrier layer of an anti-emission coating

It is established that the working life of a Pt₃Zr intermetallic anti-emission coating is determined by the mutual diffusion of free platinum atoms in the substrate and atoms of the substrate material in the coating. A multilayer coating technology has been developed, according to which a sublayer of the substrate metal carbide is initially formed that provides a barrier for the interdiffusion of platinum and substrate material. It is shown that the presence of this barrier layer significantly increases the working life of the anti-emission coating.     

Revised Kubelka-Munk theory. II. Unified framework for homogeneous and inhomogeneous optical media

We extend the applicability of the recently revised Kubelka-Munk (K-M) theory to inhomogeneous optical media by treating inhomogeneous ink penetration of the substrate. We propose a method for describing light propagation in either homogeneous or inhomogeneous layers using series representations for the K-M scattering and absorption coefficients as well as for intensities of the upward and downward light streams. The conventional and matrix expressions for spectral reflectance and transmittance values of optically homogeneous media in the K-M theory are shown to be special cases of the present framework. Three types of ink distribution-homogeneous, linear, and exponential-have been studied. Simulations of spectral reflectance predict a depression of reflectance peaks and reduction of absorption bands characteristic of hue shifts and significant reduction of saturation and, in turn, color gamut.     

Multiple cracking of a coating layer and its influence on fibre strength

Multiple cracking of a coating layer and its influence on the tensile strength of the coated fibre in the case of strong interfacial bonding were simulated by means of a Monte Carlo method. Within the range where the coating layer was weak, it was found that the weaker the coating layer, the larger became the number of cracks and consequently the smaller became the crack spacing, resulting in higher strength of the fibre. When the strength of the layer was high, however, the crack spacing became large, resulting in a low strength of the fibre comparable to the strength for the case of single cracking. The strength value of the fibre calculated for average crack spacing gave an upper bound, and that calculated for single cracking a lower bound, for the actual fibre strength.     

Multiple cracking of a coating layer and its influence on fibre strength

A calculation method to describe the influence of the non-uniform crack-spacing in a strongly adhering coating layer, which shows multiple cracking, on the energy release rate of a coated fibre is presented and applied to some examples. Four main results were found. The energy release rate of the fibre at the crack in the region of narrow crack-spacing was low. For any crack-spacing, the energy release rate was high when the Young's modulus of the fibre was low and that of the coating layer was high. From the calculation of energy release rates of the fibre at all cracks, the strength-determining crack could be identified, and from this the fibre strength after multiple cracking of the coating layer could be estimated. Finally, the strength of the fibre for non-uniform crack spacing was lower than that for a uniform one.     

Parametric method in the theory of a periodic boundary layer with large strouhal numbers

A universal equation for the Linn problem on a periodic boundary layer is obtained and solved numerically with certain values of the parameters.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 1, pp. 96–103, January, 1976.     

Calculation of pressure under a thermally stable shell in a composite coating

A method of determining the pressure under a thermally stable shell of a combined coating is examined when heated, and when a temperature, at which thermal destruction of the material takes place, is established and maintained on the surface of the thermally insulating substratum.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 6, pp. 1115–1118, December, 1969.