Microfluidic channels with integrated pillars are fabricated on SU8 and PDMS substrates to understand the capillary flow.
Microscope in conjunction with high-speed camera is used to capture the meniscus front movement through these channels for
ethanol and isopropyl alcohol, respectively. In parallel, numerical simulations are conducted, using volume of fluid method,
to predict the capillary flow through the microchannels with different pillar diameter to height ratio, ranging from 2.19
to 8.75 and pillar diameter to pitch ratio, ranging from 1.44 to 2.6. The pillar size (diameter, pitch and height) and the
physical properties of the fluid (surface tension and viscosity) are found to have significant influence on the capillary
phenomena in the microchannel. The meniscus displacement is non-uniform due to the presence of pillars and the non-uniformity
in meniscus displacement is observed to increase with decrease in pitch to diameter ratio. The surface area to volume ratio
is observed to play major roles in the velocity of the capillary meniscus of the devices. The filling speed is observed to
change more dramatically under different pillar heights upto 120 μm and the change is slow with further increase in the pillar
height. The details pertaining to the fluid distribution (meniscus front shapes) are obtained from the numerical results as
well as from experiments. Numerical predictions for meniscus front shapes agree well with the experimental observations for
both SU8 and PDMS microchannels. It is observed that the filling time obtained experimentally matches very well with the simulated
filling time. The presence of pillars creates uniform meniscus front in the microchannel for both ethanol and isopropyl alcohol.
Generalized plots in terms of dimensionless variables are also presented to predict the performance parameters for the design
of these microfluidic devices. The flow is observed to have a very low Capillary number, which signifies the relative importance
of surface tension to viscous effects in the present study. 相似文献
Abstract. Coplanar camera calibration is the process of determining the extrinsic and intrinsic camera parameters from a given set
of image and world points, when the world points lie on a two-dimensional plane. Noncoplanar calibration, on the other hand,
involves world points that do not lie on a plane. While optimal solutions for both the camera-calibration procedures can be
obtained by solving a set of constrained nonlinear optimization problems, there are significant structural differences between
the two formulations. We investigate the computational and algorithmic implications of such underlying differences, and provide
a set of efficient algorithms that are specifically tailored for the coplanar case. More specifically, we offer the following:
(1) four algorithms for coplanar calibration that use linear or iterative linear methods to solve the underlying nonlinear
optimization problem, and produce sub-optimal solutions. These algorithms are motivated by their computational efficiency
and are useful for real-time low-cost systems. (2) Two optimal solutions for coplanar calibration, including one novel nonlinear
algorithm. A constraint for the optimal estimation of extrinsic parameters is also given. (3) A Lyapunov type convergence
analysis for the new nonlinear algorithm. We test the validity and performance of the calibration procedures with both synthetic
and real images. The results consistently show significant improvements over less complete camera models.
Received: 30 September 1998 / Accepted: 12 January 2000 相似文献
Three series of composite films based on polyimide and MWNTs were prepared by conversion of pyromellitic dianhydride and 4,4′‐oxydianiline in the presence of the nanotubes, followed by thermal imidization. Carboxy‐ and amino‐functionalized as well as unmodified nanotubes were used. It was demonstrated that just 0.5 wt.‐% of nanotubes increased the tensile properties of the composite films distinctly. Surprisingly, a significant influence of the functional groups on the mechanical performance of the composite films could not be demonstrated. However, it was shown that functional groups may reduce the conductivity of the films. Furthermore, the influence of ultrasonication is discussed.
Product-mix of castings of different types/sizes can be produced in a heat (batch of melt) if all these castings require similar
raw material composition. However, inappropriate product-mix may lead to under utilization of furnace capacity or failure
in timely delivery or overproduction of castings or may call for deployment of excess resources for packing of molds to enable
starting of the pouring operation in time. Some objectives, again, can be conflicting in nature. This paper presents a weighted
integer goal programming model for the product-mix planning, developed in the context of a small scale iron foundry. Implementation
of the model is illustrated using real life data from an Indian foundry. 相似文献
The objective of our study is to design an expert system by modelling the knowledge and thinking process of a doctor. A fuzzy logic controller (FLC) is used to model the process and a genetic algorithm (GA) helps to select a number of good rules from a manually constructed large rule base of an FLC, based on the opinion of 10 doctors. The GA-based tuning is done off-line. Once the optimized rule base of the FLC is obtained, it can diagnose the disease, on-line. The scope of the present work has been extended to two diseases, namely Pneumonia and Jaundice. The symptoms of each disease are fed as inputs to the FLC and the output, i.e., grade of a disease is determined. 相似文献
The 3-D small-scale yielding (SSY) model provides a computational framework to study fatigue crack growth in thin, metallic components (and test specimens) containing an initially sharp, straight-through crack. This work describes a finite element study of plasticity-induced crack closure in the 3-D SSY model under mode I, constant amplitude cyclic loading with a ratio R=Kmin/Kmax. A purely kinematic hardening model with constant modulus represents the material constitutive behavior. This paper first addresses key computational issues and proposes modeling guidelines leading to 3-D numerical results for fatigue crack growth in SSY that exhibit convergence with mesh refinement. Specifically, computed crack opening loads show an independence of finite element mesh refinement when (a) the plastic zone at peak load encloses more than 10 eight-noded brick elements (b) the reverse plastic zone encloses at least two elements, and (c) the half-thickness has at least five element layers. The paper also describes stress and deformation fields at the crack front for a growing fatigue crack and provides an understanding of localized 3-D effects on the normalized remote opening load value Kop/Kmax. In addition, the computational studies demonstrate that the similarity scaling relationship established for R=0 [Roychowdhury and Dodds, Fatigue Fract. Engng. Mater. Struct. (accepted for publication)] also holds for the non-zero ratio R=0.1--a value commonly adopted in experimental programs. In particular, Kop/Kmax, at each location along the crack front remains unchanged when the peak load (Kmax), thickness (B) and material flow stress (σ0) all vary to maintain a fixed value of . 相似文献
The unusual amino acid diaminopimelic acid (DAP) was prepared by cross metathesis of appropriately protected vinyl glycine and allyl glycine derivatives. Catalytic hydrogenation of the cross-coupling product resulted in reduction of the double bond and the removal of protecting groups. The resulting compounds were appropriately protected for the polymer-supported and solution-phase synthesis of muramyl tripeptides 2 and 3, which differ in the amidation of the alpha-carboxylic acids of the isoglutamine and DAP moieties. Muramyl dipeptide (1, MDP), the DAP-containing muramyl tripeptide 3, and the lysine-containing muramyl tripeptides 4 and 5 induced TNF-alpha gene expression without TNF-alpha protein production in a human monocytic cell line. The observed block in translation could be removed by co-incubation with LPS, resulting in an apparent synergistic effect. Compound 2 did not induce TNF-alpha gene expression, neither did it exhibit a synergistic effect with LPS; this indicates that amidation of the alpha-carboxylic acids of the isoglutamine and DAP moieties results in a loss of biological activity. It is proposed that amidation of alpha-carboxylic acids is a strategy that may be used by pathogens to avoid detection by the innate immune system. Furthermore, the pattern recognition receptors Nod1 and Nod2 have been implicated in the possible induction of a synergistic effect of muropeptides with LPS. 相似文献