A heuristic for determination of optimal capacity of central storage

A system of one machine used to produce m products in batches and a central storage used for storing raw materials and finished products is considered. The system maintains enough finished products to assure no stockout will happen. The machine has a finite production rate greater than or equal to the demand rate for each product, and thus operates with periodic start-ups and shut-downs. For special case when set-up for each product requires time and every product is produced in every cycle, the best policy given limited storage space is determined, and total production cost as a function of set-up costs, carrying cost, storage cost, and material handling cost is presented. A heuristic is developed that determines “optimal feasible cycle time” such that production scheduling remains feasible, the capacity of the central storage is not exceeded, and the overall costs are minimized.     

Mechanical and thermal properties of toughened polypropylene composites

The mechanical, thermal, and structural properties of a new flexible composite containing polypropylene fiber (PP) in a random poly(propylene‐co‐ethylene) (PPE) matrix with ethylene–propylene elastomer (EP) was investigated with emphasis on the effect of EP elastomer concentration. The intrinsic composition of the composites, toughening of the matrix with EP and the fiber–matrix interface determined the properties of the composites. Through the incorporation of EP elastomer into the polypropylene–poly (propylene‐co‐ethylene) (all‐PP) composite, tensile and storage modulus (E′) decreased, flexural modulus and loss modulus (E″, damping) increased slightly to 0.15 EP and then decreased. There was an increase in impact resistance for the toughened composites, with about 100% increase in comparison with an untoughened all‐PP composite. The composition corresponding to 0.20 weight fraction EP gave optimum impact and mechanical properties. Creep resistance of the composite decreased with increasing EP content, but recovery showed an increase with increasing EP content up to 0.20. Fracture surfaces of composites after impact tests were studied with scanning electron microscopy. Moreover, the use and limitation of theoretical equations to predict the tensile and flexural modulus of the flexible PP composite is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The effect of fiber concentration on mechanical and thermal properties of fiber‐reinforced polypropylene composites

A novel composite material consisting of polypropylene (PP) fibers in a random poly(propylene‐co‐ethylene) (PPE) matrix was prepared and its properties were evaluated. The thermal and mechanical properties of PP–PPE composites were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) with reference to the fiber concentration. Although, by increasing PP fiber concentration in PPE, no significant difference was found in melting and crystallization temperatures of the PPE, the storage, and the tensile and flexural modulus of the composites increased linearly with fiber concentrations up to 50%, 1.5, 1.0, 1.3 GPa, respectively, which was approximately four times higher than that for the pure PPE. There is a shift in glass transition temperature of the composite with increasing fiber concentration in the composite and the damping peak became flatter, which indicates the effectiveness of fiber–matrix interaction. A higher concentration of long fibers (>50% w/w) resulted in fiber packing problems, difficulty in dispersion, and an increase in void content, which led to a reduction in modulus. Cox–Krenchel and Haplin–Tsai equations were used to predict tensile modulus of random fiber‐reinforced composites. A Cole–Cole analysis was performed to understand the phase behavior of the composites. A master curve was constructed based on time–temperature superposition (TTS) by using data over the temperature range from −50 to 90°C, which allowed for the prediction of very long and short time behavior of the composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2260–2272, 2005     

Mechanical and Thermal Properties of Flexible Poly(propylene) Composites

Summary: The melting temperature difference between poly(propylene) (PP) fibre and random poly(propylene‐co‐ethylene) (PPE) was exploited to establish processing conditions for all‐PP composite. Under these conditions, the matrix must be liquid to ensure good wetting and impregnation of fibres, though temperatures must be low enough to avoid melting of fibres. The high chemical compatibility of the two components allowed creation of strong physico‐chemical interactions, favouring strong interfacial adhesion. Static and dynamic mechanical properties and morphology of all‐PP composites were investigated according to method of preparation and compared with the behaviour of hot compacted composites, prepared under different moulding conditions. The composites were compacted with varying pressure and time, and mechanical and thermal properties of the resulting sheets were measured. With increased moulding time, more fibres melted or their original properties deteriorated. Fast cooling or quenching caused imperfect morphology. Moulding pressure played an important role. Morphology of the optimum hot compacted composite was investigated using scanning electron microscopy before and after tensile testing. Tensile fracture surfaces showed a melted phase epitaxially crystallised onto the remaining orientated phase. Compacted composites showed fibre shapes under a thin layer of PPE with all of the gaps between fibres filled by melted PPE matrix.

SEM of compacted all‐PP composite without quenching.     

Shading and lighting operation in office buildings in Austria: A study of user control behavior

Occupants of buildings typically operate devices such as windows, shades, luminaires, radiators, and fans to bring about desirable indoor environmental conditions. These control actions can have a significant impact on buildings’ performance (energy use, indoor climate). A better understanding of control-oriented user behavior can not only facilitate more accurate predictions of buildings’ performance, but also support the effective operation of buildings’ service systems. This paper describes a study of control-oriented user behavior (as related to systems for lighting and shading) in three office buildings in Austria. The results specifically shed light on the relationships between control actions and environmental conditions inside and outside buildings.     

Required steps for successful design and implementation of simulation

Use of simulation modeling as a tool to address manufacturing issues enables the modeler to measure the performance of the existing or proposed systems under different operating schemes. It can help management make basic evaluations of the different options. Therefore, simulation of the system's operation has rapidly become one of the most useful and common applications of computers. But, along with the prevailing use of simulation has come a great deal of misuse. Underlying all misuses is lack of knowledge. In this article the process of simulation modeling, data collection, common pitfalls in simulation modeling and its implementations, data analysis, output interpretation design of simulation experiments, and training requirements are described.     

Development of an educational facilities layout software

This paper describes a software developed for educational purposes that integrates most required procedures in design of facilities layout. It can be used to explain the steps that have to be taken in facilities planning process. The input for this program include: history of demand for the products to be manufactured, bill of materials, route sheets, elements of cost, type of layout desired, type of material handling system preferred, inventory policies implemented, and financial status of the company. The output of the program include: production capacity, number of equipment, number of skilled and unskilled labor, production cost of the product, layout of the production, service, and support facilities, size and layout of receiving and shipping, the size and layout of the storage and warehouse, number of material handlers, total area required, total capital invested and/or borrowed, and financial report.     

What Can Be Done to Screen Progressive Diseases Optimally

A stochastic model for a screening program is presented in which the natural history of the disease is assumed to progress through a set of stages before detection. A model of the whole process is developed to address the interaction of the disease process and screening process. The purpose of the model is to develop insight into the disease process and derive policies which are optimal relative to the particular objectives chosen.     

Deterioration of polyaramid and polybenzimidazole woven fabrics after ultraviolet irradiation

In this study the degradation of woven fabrics of meta‐aramid and the blend of para‐aramid and polybenzimidazole fibers when exposed to environmental conditions has been investigated under accelerated ageing conditions. Generally, these polymeric materials have been used for the outer layer of protective clothing, particularly for fire‐fighting. The performance of these fabrics plays an important role in preventing burn‐injuries to fire fighters. Frequent exposure of these materials to various environmental conditions (especially sunlight) can degrade the polymeric chain and affect their performance properties. Hence, the degradation of the fabrics has been studied in terms of loss of tensile and tear strength; reduction in abrasion resistance; and extension at break. It was observed that ultraviolet (UV) irradiation negatively impacted on the mechanical properties of both the polymeric materials significantly. This can be attributed to chemical changes in the polymeric chains due to the photo‐oxidation of the polymer. Scanning electron microscopy images revealed surface decomposition of the filaments due to UV irradiation. Exposure of polybenzimidazole resulted in rapid loss of mechanical and chemical properties in comparison with meta‐aramid. However, decomposition and degradation of polybenzidimazole was not statistically significant. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43073.     

Adolescent girls' and boys' weight-related health behaviors and cognitions: Associations with reputation- and preference-based peer status.

In this study, the authors examined associations between preference- and reputation-based peer status and weight-related behaviors and cognitions for both adolescent boys and girls. Sociometric measures of peer likability and peer-perceived popularity, as well as self-reported measures of body size, dieting behavior, and weight-related cognitions were collected from a sample of 441 adolescents in Grades 11 and 12. Results revealed weight-related cognitions for girls (concerning obesity) and boys (concerning musculature/fitness). Peer-perceived popularity, but not likability, was significantly associated with both boys' and girls' body size and dieting. Lower levels of popularity were associated with heavier body shapes for girls and with both thin and heavier body shapes for boys. Findings suggest that peer status is an important source of social reinforcement associated with weight-related behaviors and cognitions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)