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    Fuzzy control system for a remote focusing microscope

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    Space Station Crew Health Care System procedures require the use of an on-board microscope whose slide images will be transmitted for analysis by ground-based microbiologists. Focusing of microscope slides is low on the list of crew priorities, so NASA is investigating the option of telerobotic focusing controlled by the microbiologist on the ground, using continuous video feedback. However, even at Space Station distances, the transmission time lag may disrupt the focusing process, severely limiting the number of slides that can be analyzed within a given bandwidth allocation. Substantial time could be saved if on-board automation could pre-focus each slide before transmission. The authors demonstrate the feasibility of on-board automatic focusing using a fuzzy logic ruled-based system to bring the slide image into focus. The original prototype system was produced in under two months and at low cost. Slide images are captured by a video camera, then digitized by gray-scale value. A software function calculates an index of 'sharpness' based on gray-scale contrasts. The fuzzy logic rule-based system uses feedback to set the microscope's focusing control in an attempt to maximize sharpness. The systems as currently implemented performs satisfactorily in focusing a variety of slide types at magnification levels ranging from 10 to 1000x. Although feasibility has been demonstrated, the system's performance and usability could be improved substantially in four ways: by upgrading the quality and resolution of the video imaging system (including the use of full color); by empirically defining and calibrating the index of image sharpness; by letting the overall focusing strategy vary depending on user-specified parameters; and by fine-tuning the fuzzy rules, set definitions, and procedures used

    Strength and flexibility properties of advanced ceramic fabrics

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    The mechanical properties of four advanced ceramic fabrics are measured at a temperature range of 23 C to 1200 C. The fabrics evaluated are silica, high-and low-boria content aluminoborosilicate, and silicon carbide. Properties studied include fabric break strengths from room temperature to 1200 C, and bending durability after temperature conditioning at 1200 C and 1400 C. The interaction of the fabric and ceramic insulation is also studied for shrinkage, appearance, bend resistance, and fabric-to-insulation bonding. Based on these tests, the low-boria content aluminoborosilicate fabric retains more strength and fabric durability than the other fabrics studied at high temperature

    Constraints on scalar diffusion anomaly in three-dimensional flows having bounded velocity gradients

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    This study is concerned with the decay behaviour of a passive scalar θ\theta in three-dimensional flows having bounded velocity gradients. Given an initially smooth scalar distribution, the decay rate d/dtd/dt of the scalar variance is found to be bounded in terms of controlled physical parameters. Furthermore, in the zero diffusivity limit, κ0\kappa\to0, this rate vanishes as κα0\kappa^{\alpha_0} if there exists an α0(0,1]\alpha_0\in(0,1] independent of κ\kappa such that <<\infty for αα0\alpha\le\alpha_0. This condition is satisfied if in the limit κ0\kappa\to0, the variance spectrum Θ(k)\Theta(k) remains steeper than k1k^{-1} for large wave numbers kk. When no such positive α0\alpha_0 exists, the scalar field may be said to become virtually singular. A plausible scenario consistent with Batchelor's theory is that Θ(k)\Theta(k) becomes increasingly shallower for smaller κ\kappa, approaching the Batchelor scaling k1k^{-1} in the limit κ0\kappa\to0. For this classical case, the decay rate also vanishes, albeit more slowly -- like (lnPr)1(\ln P_r)^{-1}, where PrP_r is the Prandtl or Schmidt number. Hence, diffusion anomaly is ruled out for a broad range of scalar distribution, including power-law spectra no shallower than k1k^{-1}. The implication is that in order to have a κ\kappa-independent and non-vanishing decay rate, the variance at small scales must necessarily be greater than that allowed by the Batchelor spectrum. These results are discussed in the light of existing literature on the asymptotic exponential decay eγt\sim e^{-\gamma t}, where γ>0\gamma>0 is independent of κ\kappa.Comment: 6-7 journal pages, no figures. accepted for publication by Phys. Fluid
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