Application of fiber optic sensors to fracture mechanics problems

An experimental study is conducted to show the application of fiber optic sensors to fracture mechanics problems. Mode I stress intensity factors are obtained using single mode optical fibers in single edge notched specimens fabricated from aluminium. A Mach–Zehnder interferometric set up is used during the experiments. The experimental results compare well with theoretical predictions.     

Determination of unit load sizes in an AGV-based material handling system for an FMS

Unit load size is a key factor in an automated guided vehicle based material handling system for a flexible manufacturing system. Highlighting this aspect and its importance at the design stage, this paper presents an integer programming formulation of the problem of finding the optimal unit load size. Using an existing analytical model to decide the number of AGVs required, an algorithm based on branching and implicit enumeration and a heuristic have been developed. Revised computations due to dynamic system conditions such as changes in part mix are also possible with the proposed algorithms. The methodologies have been demonstrated using numerical examples.     

Complexity of unification problems with associative-commutative operators

The unification problem for terms containing associative and commutative functions is of importance in theorem provers based on term rewriting and resolution methods as well as in logic programming. The complexity of determining whether two such terms are unifiable was known to be NP-hard. It is proved that the problem is NP-complete by describing a nondeterministic polynomial time algorithm for it. The case where the terms are linear and have no common variables is shown to be in P. The NP-completeness of other similar unification problems, in particular, when a function symbol is also idempotent and/or has a unit (identity), is also discussed. Finally, a table of the complexity of E-matching and E-unification problems is given.Partially supported by the National Science Foundation grant nos. DCR-8408461 and CCR-8906678. A preliminary version of this paper appeared earlier as a technical report of General Electric Corporate Research and Development, Dec. 1986.     

Development of immortalized human cerebromicrovascular endothelial cell line as an in vitro model of the human blood-brain barrier

The objective of this study was to generate an immortal cell line representative of specialized human brain microvascular endothelia forming the blood-brain barrier (BBB) in vivo. Human capillary and microvascular endothelial cells (HCEC) were transfected with the plasmid pSV3-neo coding for the SV40 large T antigen and the neomycin gene. The neomycin-resistant transfected cells overcame proliferative senescence, and after a 6-8 wk period of crisis produced immortalization-competent cell colonies. Single-cell clones of near-diploid genotype were isolated from these colonies, propagated, and characterized. Immortalized HCEC (SV-HCEC) exhibited accelerated proliferation rates, but remained serum and anchorage dependent and retained the characteristic cobblestone morphology at confluence. SV-HCEC displayed a stable nuclear expression of SV40 large T antigen, lacked the invasiveness of transformed cells, and maintained major phenotypic properties of early passage control cells including expression of factor VIII-related antigen, uptake of acetylated low-density lipoprotein, binding of fluorescently labeled lectins, expression of transferrin receptor and transferrin receptor-mediated endocytosis, and high activities of the BBB-specific enzymes alkaline phosphatase and gamma-glutamyl transpeptidase. The diffusion of radiolabeled sucrose across SV-HCEC monolayers was fivefold lower than that observed with human lung microvascular endothelial cells. Furthermore, media conditioned by fetal human astrocytes increased the transendothelial electrical resistance of SV-HCEC monolayers by 2.5-fold. Therefore, this newly established human cell line expressing the specialized phenotype of BBB endothelium may serve as a readily available in vitro model for studying the properties of the human BBB.     

Selection of optimal machining parameters for hexapod machine tool

Parallel kinematic machine tools (PKM) have the advantages of higher stiffness, higher payload capacity and lower inertia. Still their penetration into the machine tool industry is very less. One of the difficulties in using PKMs such as hexapod machine tools is that the stiffness continuously varies with configuration change at every instant. This makes location of work piece and selection of machining parameters difficult and complicated. A methodology is presented in this article to select optimal machining parameters for hexapod machine tools. Particle swarm optimization is used as a tool in the optimization process. A profile-milling example is also presented to demonstrate the selection of machining parameters.     

Adsorption of 2,4-dichlorophenol on metal-nitrate modified activated carbon

To remove 2,4-dichlorophenol (2,4-DCP) from aqueous solution, the surface of the activated carbon was first treated with HCl and then the surface was modified by using various metal ions (Cu, Co, Fe, Ni, Zn, and Mg). Metal doping significantly enhanced the adsorption efficiency of activated carbon, an effect that was further increased by HCl treatment of the modified activated carbons. Of all the preparations, the zinc(II)-modified activated carbon with HCl treatment showed the highest adsorption capacity for 2,4-DCP. Analysis of the zinc(II)-modified activated carbon by SEM and BET showed a surface area and micropore volume of around 1,154.69 m²/g and 0.291 cm³/g, respectively, values about 20% higher than in the starting material. In the pH range of 2.0–11.0, the maximum uptake of 2,4-DCP from an initial concentration of 1,000 mg/L was 508 mg/g at pH 4.0.     

CFD analysis of water gas shift membrane reactor

Fuel cell based modular power generation can be achieved by miniaturization and process intensification of equipments in the process. Fuel cells require hydrogen rich gas which can be generated through reforming and water gas shift reaction. The water gas shift reactor being kinetically limited occupies more volume to achieve the required CO conversion. A membrane reactor integrates the reaction and hydrogen separation stages and hence reduces the volume requirement. Computational Fluid Dynamics offers virtual prototyping of the reactor and thus helps in design, optimization and scale up of reactors. In this study customized User Defined Functions (UDFs) were developed to analyze the performance of low temperature water gas shift membrane reactor. The models were validated using literature data for the parameters – synthesis gas compositions, time factor, sweep flow rate and steam to CO ratio. The effect of all these parameters on the reactor was analyzed for CO conversion, H₂ recovery, DaPe, concentration polarization, concentration profiles and conversion index. The simulations have showed that the UDFs developed were capable of simulating the membrane reactor and this can be used for the design and optimization of the membrane reactor for any process conditions.     

Experimental analysis of a two‐axis tracking system for solar parabolic dish collector

In this paper, an attempt has been made to develop a two‐axis tracking system for solar parabolic dish concentrator and experimentally evaluated the performance of the tracking system. In this proposed design, the sensor design uses the illumination produced by the convex lens on the apex of a pyramid to align the dish in‐line with the sun. The change in incident angle of the solar rays on the lens surface shifts the area of illumination from the apex of the pyramid towards its faces. Photodiodes placed on the faces of the pyramid are used as the sensitive elements to detect the movement of the sun. The sensor output is fed to a microcontroller‐based system to drive the stepper motor on the basis of the programmed algorithm such that it receives normal incidence of sunlight on the sensor. To evaluate the performance of the proposed system, a conventional available 1‐W photovoltaic (PV) panel is placed at the focal point to measure the short circuit current and open circuit voltage. With respect to the conventional solar PV panel, it is observed that the positioning accuracy of the proposed tracking system enhances the short circuit current of 0.11 A by 86%. Thus, the proposed tracking system can be used in a stand‐alone parabolic dish with concentrating PV module as the focal point for further studies.     

A model for planning the product portfolio and launch timings under resource constraints

Product design is increasingly becoming a critical function in many organisations having significant impact on their performance. It aims at the selection of a near-optimal mix of products and attribute-levels to offer in the target market. The standard product portfolio planning approach has focused on selecting optimum product profiles based on part-worth utility data. However, given that product development happens in multiple stages, combining the product definition decisions with the product development feasibility will provide organisations with a more inclusive and global solution. This paper considers a resource-constrained environment with a multi-stage product development cycle and presents an approach for helping an organisation to select the definitions of products for its product portfolio and the feasible launch timings. The proposed framework will aid product managers and researchers to identify and evaluate alternative product definitions using a Mixed Integer Linear Programming model in order to determine the alternatives which best balance product features and product development.     

Elastostatic interaction of multiple arbitrarily shaped cracks in plane inhomogeneous regions

A numerical technique has been developed for the determination of stress fields associated with multiple arbitrarily shaped cracks in plane inhomogeneous regions. The procedure allows the elastostatic analysis of cracks interacting with one or more straight bimaterial interfaces; of cracks located near, or emanating from, circular inclusions; and of cracks that emanate from single or multiple origins. The cracks may be branched or blunted, and may be subjected to arbitrarily applied stresses. The technique employs an efficient surface integral method, using distributions of edge dislocations to represent the cracks. The resulting singular integral equations are solved using a Gauss-Chebyshev integration formula; appropriate conditions are developed for closing the set of equations governing cracks intersecting inhomogeneity boundaries, based on a consideration of the stresses and displacements at the points of intersection. Crack-tip stress intensity factor results are presented for several crack configurations. The overall scheme provides a more general, direct, and convenient approach than other available schemes. A computer program has been developed to implement the various formulations in a single framework.