Modeling and solving mixed-model assembly line balancing problem with setups. Part I: A mixed integer linear programming model

This paper is the first one of the two papers entitled “modeling and solving mixed-model assembly line balancing problem with setups”, which has the aim of developing the mathematical programming formulation of the problem and solving it with a hybrid meta-heuristic approach. In this current part, a mixed-integer linear mathematical programming (MILP) model for mixed-model assembly line balancing problem with setups is developed. The proposed MILP model considers some particular features of the real world problems such as parallel workstations, zoning constraints, and sequence dependent setup times between tasks, which is an actual framework in assembly line balancing problems. The main endeavor of Part-I is to formulate the sequence dependent setup times between tasks in type-I mixed-model assembly line balancing problem. The proposed model considers the setups between the tasks of the same model and the setups because of the model switches in any workstation. The capability of our MILP is tested through a set of computational experiments. Part-II tackles the problem with a multiple colony hybrid bees algorithm. A set of computational experiments is also carried out for the proposed approach in Part-II.     

Increasing single-lap joint strength by adherend curvature-induced residual stresses

Single-lap joint (SLJ) geometry is the most widely used type of adhesive joint geometry. In this joint, peel stresses occur at the overlap ends due to load eccentricity and the presence of shear-free adhesive termination surfaces. These peel stresses, along with the transverse tensile stresses which occur along the overlap longitudinal axes, and adhesive shear stresses, ultimately cause joint failure. Obviously, reductions in these stresses should result in higher joint strength and increased load capacity. To this end, we exploited elastic spring-back capability of (steel) metal adherends by initially forming curved segments of varying arc lengths and radii at overlap ends. These adherends with curved-end sections were then bonded in single-lap configuration, simply by applying sufficient bonding pressure to elastically flatten the curved segments to result in typically flat overlap sections subsequent to adhesive cure and the removal of bonding pressure. Since the elastic adherend overlap ends tend to revert back to their initial curved form, they exert compressive residual stresses on the adhesive layer in the overlap end regions. We determined that the compressive residual stresses induced in this fashion considerably increased the load capacity of SLJs subjected to tension.     

Effect of different surface shapes formed by femtosecond laser on zirconia-resin cement shear bond strength

Objective: The purpose of this study was to evaluate the effect of different surface shapes formed by femtosecond (FS) laser on zirconia (Y-TZP)-resin cement shear bond strength (SBS). Background data: All ceramic restoration is used as an alternative to metal-ceramic restorations, due to its better aesthetics, strength, and toughness properties. However, bond strength of restoration to tooth and other materials is effective to long term success of the restoration, and to achieve it surface treatment is required on ceramic surface. Materials and methods: Forty square-shaped zirconia samples were prepared and assigned to four groups of 10. The details of the groups are as follows: Group A, square-shaped recessed surface; Group B, square-shaped projection surface; Group C, circular-shaped recessed surface; Group D, circular-shaped projection surface. The SBSs values were performed with a universal testing machine at a crosshead speed of 1 mm/min. The data were analyzed statistically using analysis of variance (ANOVA) and Tukey HSD multiple comparisons tests. Results: The one-way ANOVA results on SBSs of the zirconia material bonded with resin cement revealed significant differences among the groups (p < 0.05). The Tukey HSD test results revealed that Group B and D had significantly higher SBS values than other groups (p < 0.05), but there were no significant differences between each other (p > 0.05). Additionally, Group A and C had significantly lower values than other groups (p < 0.05). Conclusions: Different surface shapes formed by FS laser provided a significant increase in SBSs. The SBS values of projection surfaces of circular and square-shapes are greater than that of recessed surfaces of circular and square-shapes.     

Improvement of enzymatic xylooligosaccharides production by the co-utilization of xylans from different origins

This study aimed to improve XOs production by enzymatic hydrolysis of xylans from various lignocellulosic waste biomasses namely corn cob, cotton and sunflower stalks, rice hull, wheat straw by using two commercial xylanase preparations, Shearzyme 500L and Veron 191. Shearzyme 500L showed better xylan hydrolysis capacity with high amount of xylose liberation. Xylobiose was the main hydrolysis product in each case. Even though the enzymatic hydrolyses using Shearzyme 500L resulted higher reducing sugar production compared to those of Veron 191, the hydrolysis of complex xylan structures was improved and the production of undesirable xylose was lowered by the co-utilization of xylanase preparations. By the co-utilization of xylanase preparations, the reducing sugar production from wheat straw, corn cob and sunflower stalk originated xylans was increased by 36%, 33% and 13%, respectively, compared to the expected reducing sugar yields. The highest reducing sugar production was obtained from complex corn cob xylan. The depolymerization of cotton and sunflower stalk xylan was poorest even though they have simple structures. Poor utilization of these xylans might be related to their high residual lignin content which might hinder the accessibility of xylan by the xylanases. However, the utilization of sunflower and cotton stalk xylan was improved when they were hydrolyzed within a xylan mixture containing equal amounts of each of five different xylans. In short, XOs production efficiency from agricultural waste materials was improved by the co-utilization of suitable xylanase and/or xylan mixtures considering the heterogeneous structures of xylan and different substrate specificities of xylanases.     

A simple technical modification for abdominal cardiac transplantation in rats

We report herein the first laboratory-diagnosed case of Lyme disease in a human in Taiwan. A 45-year-old Taiwanese man living in Taipei, in northern Taiwan, had an expanding skin lesion (measuring 23 by 15 cm) on his abdomen for 2 to 3 weeks and recurrent attacks of pain and swelling of the knee joint. Serologic tests indicated a significantly elevated titer of antibody to Borrelia burgdorferi. After appropriate antibiotic treatment for 3 weeks, the skin lesion was cured and the joint swelling was improved. Although several strains of Borrelia spirochetes had been isolated from rodents (Rattus losea) in Taiwan, the tick vector responsible for the transmission remains to be identified.     

The effect of using a whey protein fat replacer on textural and sensory characteristics of low-fat vanilla ice cream

The purpose of this research was to evaluate the texture of regular (12%), low fat (6%), and fat-free vanilla (0.5%) ice creams by sensory and instrumental analyses. The low fat and fat free ice cream were prepared using a whey protein based fat replacer (Simplesse ^® 100) as the fat replacement ingredient. Two processing trials with continuous commercial-like process conditions were undertaken. Sensory analyses disclosed that ice creams containing 6% of fat replacer in place of or with milk fat had no demonstrable effect on vanillin flavour. While the sensory attributes of the low fat samples were comparable to the regular vanilla ice cream, the trained sensory panel rated the fat free ice cream to have lower viscosity, smoothness and mouth coating properties. Instrumentally determined apparent viscosity data supported the sensory data. Compared with the fat replacer, milk fat significantly increased the fresh milk and cream flavours of the ice cream. Results emphasized the importance of fat as a flavour modifier and the improvement of texture by addition of Simplesse ^® 100.     

Calculation of the overlap angle in slip energy recovery drivesusing a d,q/abc model

A closed-form expression for estimating the overlap angle in a slip energy recovery system is presented. The prediction of the overlap angle is important in the case of doubly-fed induction motor drives, because of its influence on speed and torque. A closed-form expression is derived using a hybrid model of the induction motor and a dynamic model of the rotor rectifier. The ripple content of the DC link current and the inverter input voltage are neglected. The results predicted by the closed-form expression are verified experimentally