Rheological behavior of functional sugar-free guava preserves: Effect of the addition of salts

The addition of salts to carrageenan and locust bean gum gels functions to improve the characteristics of texture, thereby increasing gel strength. This effect is widely studied in gels of model systems but is studied to a lesser extent in complex systems, such as fruit preserves. The objective of this study was to evaluate the effect of adding salts on the rheological behavior of functional sugar-free guava preserves, as well as to correlate the rheological parameters. To this end, three types of texture properties were analyzed (texture profile, stress relaxation and uniaxial compression) in functional sugar-free guava preserves prepared with different concentrations of KCl and CaCl₂ salt. The analyses were performed with a texturometer (Stable Micro Systems, Model TA - XT2i), and the parameters were analyzed using a Scott-Knott test at 5% probability, principal components analysis and Pearson correlation. CaCl₂ was more effective for improving the characteristics of texture, especially gel strength (concentration near the F3: 0.33%), whereas KCl addition degraded gel strength. In the analysis of test relaxation, the Maxwell model parameters provided better discrimination between samples than the Peleg model parameters. Positive and negative correlations were observed, and the parameters of hardness, adhesiveness and elastic modulus ideal (E₁) were the most correlated with other rheological parameters.     

The Influence of Calcite,Fluorite, and Rutile on the Fusion-Related Behavior of Metal Cored Coated Electrodes for Hardfacing

Coated electrodes for SMAW have exhibited their advantages for longer than one century. Means of boosting their performance, particularly for hardfacing, would be a raise in the alloying transfer efficiency and a lowering of the dilution with the substrate, without losing the production capacity. In this study, an evaluation about the operational behavior of a new conception of electrodes for hardfacing is described, i.e., metal cored coated electrodes. Experimental electrodes were produced using metal cored technique to obtain the rods. FeCrMn was used as alloying material at two grain sizes. Using the Mc Lean Anderson experimental design approach, the content ratio of CaCO₃:CaF₂:TiO₂ in the coating was varied. The effect of the coating composition and granulometry of the filling alloying material on the formation a cannon-like end was assessed. Fusion and metal transfer behaviors were evaluated through measurements of fusion and deposition rates, deposition efficiency, and duration and frequencies of short-circuiting. Based on a balance of performances, the most appropriate composition for the coating was determined. It was also observed that a coarser FeCrMn presented better performance.     

Black box scatter search for general classes of binary optimization problems

The purpose of this paper is to apply the scatter search methodology to general classes of binary problems. We focus on optimization problems for which the solutions are represented as binary vectors and that may or may not include constraints. Binary problems arise in a variety of settings, including engineering design and statistical mechanics (e.g., the spin glass problem). A distinction is made between two sets of general constraint types that are handled directly by the solver and other constraints that are addressed via penalty functions. In both cases, however, the heuristic treats the objective function evaluation as a black box. We perform computational experiments with four well-known binary optimization problems to study the efficiency (speed) and effectiveness (solution quality) of the proposed method. Comparisons are made against both commercial software and specialized procedures on a set of 376 instances. We chose commercial software that is similar in nature to the proposed procedure, namely, it treats the objective function as a black box and the search is based on evolutionary optimization techniques.     

Evaluating the use of self-assembled monolayer (SAM) release coatings for replicated optics

Carbon fiber-reinforced composite replicated mirrors offer weight savings, higher stiffness, tailorable CTEs, higher thermal conductivities, and excellent damage tolerant mechanical properties in comparison to traditionally processed glass mirrors. These mirrors can also be rapidly manufactured by replicating the surface of a high-precision glass mandrel multiple times. The mold release coating used is critical and must be on the molecular scale, uniform, and exhibit low adhesion in order to produce high-fidelity replication. This study investigates the use of a self-assembled monolayer (SAM) as the mold release agent for the manufacture of replicated mirrors. We have synthesized and tested perfluoropolyether (PFPE) coatings formed on glass substrate via self-assembly. Ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy were used to characterize the morphology, thickness uniformity and the chemical profile of the coatings. The release force necessary to remove the replicated surfaces from the mandrel is critical and was directly related to the surface distortion of the replica. The release force increased with each successive replication due to pinholes and defects. Incorporating a secondary, lower molecular weight SAM reagent significantly reduced both surface agglomeration and transfer of SAM material to the replicated resin surface. A 60% reduction in the replica release force and a 50% improvement in the replica surface figure were achieved due to reductions in the defect density of the SAM coating.     

Comparing mechanical behaviour of aluminium welds produced by laser beam welding (LBW), friction stir welding (FSW), and riveting for aeronautical structures

Three welding processes for aluminium parts have been considered for aircraft fabrication: riveting, friction stir welding (FSW) and laser beam welding (LBW). These processes have advantages and threats, which were analysed in the present work focusing on T-pull and Hoop tensile properties. Concerning T-pull tests, LBW coupons presented higher ability to withstand the applied loads. This was due to the better distribution of loads when the strain is done in the stringer direction. In the case of the Hoop tests, which stress only the skin, the results obtained after FSW were notably higher in terms of ultimate tensile stress, yield stress and maximum strain. It was concluded that both LBW and FSW could replace riveting usually applied for commercial aircraft manufacturing.     

Cyclodextrin Insulation Prevents Static Quenching of Conjugated Polymer Fluorescence at the Single Molecule Level

Conjugated polymers (CPs) are promising materials for fluorescence imaging application. However, a significant problem in this field is the unexplained abnormally low fluorescence brightness (or number of fluorescence photons detected per one excitation photon) exhibited by most of CP single chains in solid polymer hosts. Here it is shown that this detrimental effect can be fully avoided for short chains of polyfluorene‐bis‐vinylphenylene (PFBV) embedded in a host polymer matrix of PMMA, if the conjugated backbone is insulated by cyclodextrin rings to form a polyrotaxane (PFBV‐Rtx). Fluorescence kinetics and quantum yields are measured for the polymers in liquid solutions, pristine films, and solid PMMA blends. The fluorescence brightness of PFBV‐Rtx single chains dispersed in a solid PMMA is very close to that expected for a chain with 100% fluorescence quantum yield, while the unprotected PFBV chains of the same length possess 4 times lower brightness. Despite this, the fluorescence decay kinetics are the same for both polymers, suggesting the presence of static or ultrafast fluorescence quenching in the unprotected polymer. About 80% of an unprotected PFBV chain is estimated to be completely quenched. The hypothesis is that the cyclodextrin rings prevent the quenching by working as ‘bumpers’ reducing the mechanical forces applied by the host polymer to the conjugated backbone and help retaining its conformational freedom. While providing a recipe for making CP fluorescence bright at the single‐molecule level, these results identify a lack of fundamental understanding in the community of the influence of the environment on excited states in conjugated materials.