The effect of Fe3O4 nanoparticles on the thermal conductivities of various base fluids

Conventional heat transfer fluids have intrinsically poor heat transfer properties compared to solids. Enhancing the efficiency of heat transfer is of great interest for various industrial applications. Suspending solid particles in a fluid increases the thermal conductivity of the resulting suspension and enhances the heat transfer properties. In this work, changes in thermal conductivities of fluids upon the addition of magnetic nanoparticles have been investigated. Fe(3)O(4) nanoparticles are synthesized using different synthesis methods and are suspended in various oils. The effect of the base fluid and the type of magnetic particle on the thermal conductivity is investigated in detail. Up to 28% increase in the thermal conductivity is obtained with 2.5 wt% magnetic particles in hexane. The thermal conductivity enhancement is found to depend on the particle concentration, method of preparation and base fluid. The enhancements obtained are higher than those estimated using any theoretical model present in the literature.     

New secretory strategies for Kluyveromyces lactis {beta}-galactosidase

We examined several strategies for the secretion of Kluyveromyceslactis ß-galactosidase into the culture medium, inorder to facilitate the downstream processing and purificationof this intracellular enzyme of great industrial interest. Weconstructed plasmids by fusing the LAC4 gene or engineered variantsto the secretion signal of the K.lactis killer toxin or to thesecretion signal of the Saccharomyces cerevisiae -factor. Withthese plasmids we transformed strains of the yeasts K.lactisand S.cerevisiae, respectively and tested ß-galactosidaseextracellular activity in different culture media. We achievedpartial secretion of ß-galactosidase in the culturemedium since the high molecular weight and oligomeric natureof the enzyme, among other factors, preclude full secretion.The percentage of secretion was improved by directed mutagenesisof the N-terminus of the protein. We developed several deletionmutants which helped us to propose structure–functionrelationships by comparison with the available data on the homologousEscherichia coli ß-galactosidase. The influence ofthe culture conditions on heterologous ß-galactosidasesecretion was also studied.     

Assembly line balancing with positional constraints,task assignment restrictions and station paralleling: A case in an electronics company

In this paper, we present a real-life Assembly Line Balancing Problem for an electronics manufacturing company. The main characteristics of the problem are as follows: (i) a set of operations are related to the front part of the workpiece and others are related to the back part of the workpiece, which in turn makes all tasks dependent on the position of the workpiece, (ii) some of the tasks must be executed on the same station and no other tasks should be assigned to this station due to technological restrictions, (iii) parallel stations are allowed to increase the line efficiency at the required production rate and to overcome the problem of assigning tasks with operation times that exceed the cycle time. Initially, the problem is formulated as a 0–1 integer programming model and solved using CPLEX solver. Then, the effect of alternative work schedules such as multiple shifts and overtime on the expected labor cost of the line is analyzed. Considering alternative work schedules while balancing the line for corresponding cycle times allows us to select an efficient assembly line for the company, resulting in a lower labor cost and a more balanced line with respect to the operation times and the activity of the workers at each station. Lastly, a computational study is conducted to evaluate the performance of the proposed model. It is found that the model is capable of producing high quality solutions in reasonable solution times.     

AR–ARCH Type Artificial Neural Network for Forecasting

Neural Processing Letters - Real-world time series such as econometric time series are rarely linear and they have characteristics of volatility. Although autoregressive conditional...     

Nested simulated annealing approach to periodic routing problem of a retail distribution system

This paper introduces a real-life variant of a periodic traveling salesman problem (V_PTSP) for a retail distribution system. A warehouse is allocated to serve specified retail districts where a large number of retailers are located and the deliveries are planned according to the visiting frequency of each retailer. The objective is to determine daily vehicle routes over a given planning period adhering to the visiting frequency restrictions while minimizing the total distance traveled. Initially, the V_PTSP is formulated as an integer programming model. Since this model can only solve small size problems, a nested simulated annealing procedure is developed for solving large size V_PTSPs. A series of computational tests are performed for evaluating the performance of the heuristic procedure. The results show that the proposed approach gives good solutions in reasonably short computation times.     

Continuous fixed bed biosorption of reactive dyes by dried Rhizopus arrhizus: determination of column capacity

A continuous fixed bed study was carried out by using dried Rhizopus arrhizus as a biosorbent for the removal of three reactive dyes; Gemacion (Procion) Red H-E7B (GR), a monoclorotriazine mono-azo type reactive dye; Gemazol Turquise Blue-G (GTB), a vinyl sulfone mono-azo type reactive dye and Gemactive (Reactive) Black HFGR (GB), a vinyl sulfone di-azo type reactive dye from aqueous solution. The effect of operating parameters such as flow rate and inlet dye concentration on the sorption characteristics of R. arrhizus was investigated at pH 2.0 and at 25 degrees C for each dye. Data confirmed that the total amount of sorbed dye decreased with increasing flow rate and increased with increasing inlet dye concentration for each dye. The column biosorption capacity of dried R. arrhizus was 1007.8 mg g(-1) for GR dye, 823.8 mg g(-1) for GTB dye and 635.7 mg g(-1) for GB dye at the highest inlet dye concentration of approximately 750 mg l(-1) and at the minimum flow rate of 0.8 ml min(-1). Thomas and Yoon-Nelson models were applied to experimental data to predict the breakthrough curves and to determine the biosorption capacity of the column for each dye useful for process design. Both models were found suitable for describing the whole dynamic behavior of the column with respect to flow rate and inlet dye concentration.     

Carbon foam production from bio-based polyols of liquefied spruce tree sawdust: Effects of biomass/solvent mass ratio and pyrolytic oil addition

One of the next-generation structural materials is carbon foam. Porous materials have become an intriguing alternative material to traditional ones in many utilizations based on their light weight and incomparable properties. Coal or fossil oils are conventionally used to produce pitch, phenolic resin, and polyurethane as carbon foam precursor. Biomass liquefaction is a developing technique to convert biomass resources into the industrial chemicals. In this study, spruce tree sawdust was liquefied under mild conditions with different solvent type (phenol or phenol + bio-oil mixture). The unique aspect of this work is the synthesis of bio-polyol when pyrolytic oil is used as an alternative to phenol in the solvolysis reaction and its evaluation in carbon foam production with multilayer graphene sheets. Therewithal, the ratios of biomass to solvent were 1/3 as well as 1/5, and the comparison of product characteristics is another originality of the study. Slow pyrolysis of spruce tree sawdust was performed under static atmosphere and bio-oil was characterized with elemental analysis and various chromatographic and spectroscopic techniques. The effect of mass ratio of biomass/solvent on the characteristics of porous resin foams synthesized from liquefaction product. Obtained resin foams were carbonized at 400 °C, and then activated at 800 °C under nitrogen atmosphere. Structure evaluation of resin foams, carbonized foams, and activated carbon foams from liquefied spruce tree sawdust was investigated by using elemental analysis, x-ray diffraction, nitrogen adsorption/desorption isotherms, scanning electron microscopy, true/bulk density, and compressive strength tests. Although the surface area values decreased when bio-oil was added as a solvent, it was determined that the compression strengths of the produced carbon foams (up to 1.080 MPa) were higher than that of conventional phenolic foams. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47185.