The mixing phenomena for two fluid streams in pressure-driven rectangular microchannels are analyzed and directly compared with the measurements of mixing intensity for a wide range of aspect ratio (width/depth = 1-20). In the analysis, the three-dimensional transport equation for species mixing was solved using the spectral method in a dimensionless fashion covering a large regime of the normalized downstream distance. The analysis reveals the details of non-uniform mixing process, which originates from the top and bottom walls of the channel and stretches out toward the center of the channel, and its transition to uniformity. Employing different length scales for the non-uniform and uniform mixing regimes, the growth of mixing intensity can be expressed in a simple relationship for various aspect ratios in the large range. The mixing experiments were carried out on silicon- and poly(methyl methacrylate) (PMMA)-based T-type micromixers utilizing fluids of pH indicator (in silicon channel) and fluorescent dye (in PMMA channel) to evaluate the mixing intensity based on flow visualization images. Using conventional microscopes, the experiments demonstrate the mixing intensity as a power law of the stream velocity for all the microfluidic channels tested. The variations of measured mixing intensity with the normalized downstream distance are found in favorable agreement with the numerical simulations. The comparison between the experiments and simulations tells the capabilities and limitations on the use of conventional microscopes to measure the mixing performance

Purpose This paper aims to propose an area under the curve model to represent ultraviolet (UV) exposure doses on EBT3 films (in mJ/cm2). The model was developed on a cross-section of the exposed films using visible absorbance method. Ultraviolet–A light emitting diodes (UVA–LEDs) with 20° and 60° half angle with distinctive peak emission wavelengths between 365 to 405 nm are used in this experiment. No similar experimental setup or findings have been reported thus far, though the various application of EBT3 for the measurement of solar UV (A + B) have been published since EBT3 is commercially available. Design/methodology/approach Two sets of UVA–LEDs were used as the UV radiation source in the experiment. The first set contains of four 5 mm low power UVA–LEDs with the 20° half angle and peak emission wavelength at 365, 375, 385 and 400 nm. The second set contains of five surface mount high power UVA–LEDs with the 60° half angle and peak emission wavelength at 365, 375, 385, 305 and 400 nm. The illumination setup for the two sets of LEDs is different between each other to obtain sufficient dose distribution on the films for spectroscopy analysis. This is due to the different illumination angle and irradiance intensity by each set of LEDs. Findings UV–LED with a peak emission of 365, 375 and 385 nm able to produce UV doses accurately measurable using EBT3 films, UVA–LEDs with peak emission at 395 nm and above produced much lower accuracy with R2. From both set of LEDs, it can be concluded that peak emission wavelength of UVA–LED does influence the discoloration of the films. Shorter wavelength (higher energy) of UVA–LEDs discolors EBT3 films much intense compared to longer wavelength for a given UV dose exposure. Originality/value Despite various practical applicability and advantages of UV–LEDs, there are still no standard methods in measuring UV–LED radiation output. The proposed approach not only allows us to obtain the dose of UV–LED, where the sensitivity of measurement is wavelength (energy) depended but also allows us to visually observe the illumination pattern of invisible UV radiation through the application of EBT3 films.

For about 3 years observati on on satellites operating in the frozen orbit round the earth, we found the eccentricity has a nearl y constant dri fting rate. The frozen orbi ts at critical inclination were part of peri odic orbits, and once supposed to be stable in eccentricity and perigee argument on average. Focusing on the 0.00033-per-year-growth eccentricity of some long-term observed critical inclination orbit, a numerical method was proposed to analyze the effects of perturbati ve force on the eccentricity, such as solar radiation pressure, third-body perturbati on and nons pherical earth gravity. Ignoring the high-order Earth gravi ty and other perturbati ve force, it was illustrated that the eccentricity drift is mai nly caused by the J5 term wi th 40% and J7 term wi th 55% in the earth gravitati on field model. Moreover, for the satellites operating on the al titude of 1100km with the perigee argument 4 o , which were affected by the high-order perturbati ve factors, the frozen eccentricity orbi t inclinati on needed to exceed 64 o and the frozen perigee-argument orbit inclination shoul d be less than 63.4 o . The dri ft was yiel ded in both the eccentricity and perigee-argument when the orbit inclination angle was between 63.4 o and 64 o . We found it's di fficult to obtain a critical orbit i nclinati on that freezing both the eccentricity and perigee argument for specified semi-major axis and perigee argument. However, the problem coul d be sol ved in hamiltonian dynamics. A hamiltoni an functi on anal ysis method was proposed to search "stable equilibrium" that corresponding to periodic orbits. The research results demonstrated that stable equilibri um drifted with high order gravity perturbation terms taken into account. If perigee argument was treated as a free parameter, we coul d find continuous periodic orbits with varying orbit inclination at specified semi-major axis.