Topological hierarchy-contour tracing algorithm for nests of interconnected contours

As a simple meaningful external illustration, a group of boundary contours is commonly used for representing the physical appearance of an object of interest on a 2D plane (e.g., a part drawing, CT scan image, a sliced layer, tile pattern). The illustration is understood from the composition of the contours and their attributes that include their shapes, sizes, locations and relationships. Therefore, not only is geometrical information important for contours to be useful in subsequent operations but their topological hierarchy relationships also are essential. Presented in this paper is a topological hierarchy-contour tracing algorithm that is capable of tracing nests of interconnected contours often found in practice and of identifying their topological hierarchy relationships automatically during contour tracing. The algorithm organizes contours by family rather than by group or as individual. However, contours are traced across families generation by generation instead of going deep with one family branch at a time. The outputs of the algorithm are ordered sequences of boundary pixels representing all closed contours and their topological hierarchy relationships. The algorithm has been implemented on LabVIEW, and tested with several samples to illustrate its applications.     

Structured light system-based selective data acquisition

Selective data acquisition has been introduced recently for direct interfacing reverse engineering (RE) with rapid prototyping (RP). Data are acquired selectively and locally layer by layer according to the analysis of an image processing algorithm that has been developed for recommending the scanning positions from the edge images of the object. The recommendations, however, depend on the quality of the input images and the edge detection parameters. An attempt to make selective data acquisition more robust and less sensitive to the aforementioned factors is therefore presented in this paper. A structured light system (SLS) and projective transformation have been integrated into this SLS-based selective data acquisition to induce features on an object surface to appear explicitly through phase distortion of a projected bright line, and to diminish perspective distortion effects in the analysis through transformation of deformed bright lines on side views to be contour segments on top view. The implementation of this new selective data acquisition approach is also presented and discussed.     

Investigation of PLA-based scaffolds fabricated via SVM rapid prototyping

Poly-lactic acid (PLA) is a biodegradable polymer that has been well accepted as a tissue engineering scaffold material. Recently, PLA has been applied in selective vacuum manufacturing (SVM), a new RP technique being developed, for fabricating scaffold. For this RP technique to be accepted for this purpose, its fabricated scaffolds must be tested for their properties. This paper presents an investigation of the properties of scaffolds fabricated from SVM technique. The results illustrated that the fabricated PLA scaffolds had porous structure. The porosity was about 71.65% with pore size ranged from 20 to 90???m. The compressive modulus of elasticity was 2.07?±?0.25?MPa, lying within the lower range of mechanical properties reported for soft tissue application. An indirect cytotoxicity test showed the cell viability of 75.92% which means that the specimens posed no threat to the cells and could be used as scaffolds for mammalian tissue culture.     

Automatic single-line drawing creation from a paper-based overtraced freehand sketch

Freehand sketching on a paper is commonly found to be used as it is a natural and intuitive communication channel for portraying ideas. Additional strokes are often drawn over the existing ones to make the sketch clearer. For its usefulness in subsequent steps, a sketch is transformed to be a 3D CAD model that is typically performed manually by a designer due to a lack of technology support. Geometrical reconstruction from an offline scanning of a sketch has been a challenge because enriched information obtained during sketching is reduced to a batch of data points. This paper presents an algorithm for identifying a single-line drawing from a paper-based overtraced sketch as it is the first important step towards geometrical reconstruction. Key activities in this approach are thick-line sketch creation, contour boundary extraction, segments identification, and line drawing creation. The algorithm has been successfully implemented on LabVIEW and tested with several samples.     

Gas Sparger Orifice Sizes and Solid Particle Characteristics in a Bubble Column – Relative Effect on Hydrodynamics and Mass Transfer

The relative effects of the size of gas sparger orifices and properties of solid particles on gas‐liquid mass transfer are not yet fully understood. Here, the impact of sparger orifice sizes, solid particle shapes, and their loading amounts in a bubble column reactor on the absorption of oxygen in tap water was investigated. Their influence on the mass transfer coefficient and bubble hydrodynamic parameters was evaluated. The results show that the addition of solid particles can have both positive and negative effects on hydrodynamics and mass transfer, depending on the orifice size of the gas sparger. The introduction of ring‐shaped solid particles can improve the mass transfer rate by up to 28 % without requiring any significant additional power.     

Recommended slicing positions for adaptive direct slicing by image processing technique

Build time and accuracy are two contradicting issues that have been a major concern in rapid prototyping, and have led to the development of many slicing approaches including those applying adaptive slicing, direct slicing, and adaptive direct slicing concepts. Presented in this paper is an approach for adaptive direct slicing that applies image processing technique to determine appropriate thickness for each sliced layer and to recommend slicing positions on a 3D CAD model. Two orthogonal views of a model are captured and converted to be edge images before being analyzed, and based on the surface complexity on the two edge images, slicing positions are recommended. These positions are passed to the CAD software for slicing activities. This adaptive direct slicing approach has been implemented on LabVIEW platform and compared with uniform direct slicing approach and uniform cusp height approach. The results show that this slicing approach improved slicing performance by reducing the number of layer which has a direct impact on build time while maintaining surface quality at the same level as the thin uniform direct slicing. Since its inputs are the images of a CAD model instead of the model itself, this adaptive direct slicing supports any CAD software.     

A new algorithm for tracing nests of interconnected contours

Boundary contour, a meaningful external representation of area of interest, is widely used in many manufacturing applications (e.g., part machining, rapid prototyping, cutting and packing of irregular shape patterns, and geometrical reconstruction), and appearing on an image, in many cases, are nests of interconnected contours that their information is typically required prior to subsequent manufacturing operations being performed. Presented in this paper is a new contour tracing algorithm for extracting nests of interconnected contours. The algorithm is capable of recognizing junctions between contours sharing common edges and of recommending, among alternatives, a path to proceed to obtain all interconnected contours. Morphological operations have been applied instead of component labeling to achieve the locations of nested contours on an image. The input to the algorithm is a binary image of 1-pixel-wide closed contours, and the outputs are ordered sequences of boundary pixels representing all closed contours. The algorithm has been implemented on LabVIEW, experimented with several contour patterns, and demonstrated its application in manufacturing.     

Effect of surfactants on liquid-side mass transfer coefficients

In the present paper, the effect of liquid properties (surfactants) on bubble generation phenomenon, interfacial area and liquid-side mass transfer coefficient was investigated. The measurements of surface tension (static and dynamic methods), of critical micelle concentration (CMC) and of characteristic adsorption parameters such as the surface coverage ratio at equilibrium (s_e) were performed to understand the effects of surfactants on the mass transfer efficiency. Tap water and aqueous solutions with surfactants (cationic and anionic) were used as liquid phases and an elastic membrane with a single orifice as gas sparger. The bubbles were generated into a small-scale bubble column. The local liquid-side mass transfer coefficient (k_L) was obtained from the volumetric mass transfer coefficient (k_La) and the interfacial area (a) was deduced from the bubble diameter (D_B), the bubble frequency (f_B) and the terminal bubble rising velocity (U_B). Only the dynamic bubble regime was considered in this work (Re_OR=150-1000 and We=0.002-4).This study has clearly shown that the presence of surfactants affects the bubble generation phenomenon and thus the interfacial area (a) and the different mass transfer parameters, such as the volumetric mass transfer coefficient (k_La) and the liquid-side mass transfer coefficient (k_L). Whatever the operating conditions, the new k_La determination method has provided good accuracy without assuming that the liquid phase is perfectly mixed as in the classical method. The surface coverage ratio (s_e) proves to be crucial for predicting the changes of k_L in aqueous solutions with surfactants.     

Hydrogen recovery from the electrocoagulation treatment of dye-containing wastewater

In this paper, a technique of hydrogen recovery from an electrocoagulation process treating dye-containing wastewater is presented. The electrocoagulation system used consists of a continuous-mode electrocoagulator connected with a gas separation tank and two sedimenters. It is shown that a significant amount of hydrogen can be harvested using the gas separation tank whose configuration follows that of a conventional upflow anaerobic sludge bed. The experimental hydrogen yields obtained were comparable with those calculated from theory. The electrical energy demand of the electrocoagulation process for treating Reactive Blue 140 and Direct Red 23 was 1.42 and 0.69 kWh_e m⁻³, respectively, while the energy yield of harvested hydrogen was 0.2 kWh m⁻³. The quality of water treated by the electrocoagulation system was satisfactory, i.e., the color, COD and TS removal were 99%, 93% and 89%, respectively.     

Ecological consequences of chemically mediated prey perception

To locate food, mobile consumers in aquatic habitats perceive and move towards sources of attractive chemicals. There has been much progress in understanding how consumers use chemicals to identify and locate prey despite the elusive identity of odor signals and the complex effects of turbulence on chemical dispersion. This review highlights how integrative studies on behavior, fluid physics, and chemical isolation can be fundamental in elucidating mechanisms that regulate species composition and distribution. We suggest three areas where further research may yield important ecological insights. First, although basic aspects of stimulatory molecules are known, our understanding of how consumers identify prey from a distance remains poor, and the lack of studies examining the influence of distance perception on food preference may result in inaccurate estimation of foraging behavior in the field. Second, the ability of many animals to find prey is greatest in unidirectional, low turbulence flow environments, although recent evidence indicates a trade-off in movement speed versus tracking ability in turbulent conditions. This suggests that predator foraging mode may affect competitive interactions among consumers, and that turbulence provides a hydrodynamic refuge in space or time, leading to particular associations between predator success, prey distributions, and flow. Third, studies have been biased towards examining predator tracking. Current data suggest a variety of mechanisms prey may use to disguise their presence and avoid predation; these mechanisms also may produce associations between prey and flow environments. These examples of how chemical attraction may mediate interactions between consumers and their resources suggest that the ecology of chemically mediated prey perception may be as fundamental to the organization of aquatic communities as the ecology of chemical deterrence.