Lithium disilicate glass produced at high pressure: Characterization of structural,thermal and mechanical properties

In this work, high-density lithium disilicate (LS₂) vitreous systems were produced by melting and quenching under high pressure (7.7 GPa) following two distinct experimental routes. In the first case, LS₂ glass was remelted at 7.7 GPa and 1600°C and, then, quenched. In the second case, a stoichiometric mixture of precursor oxides (Li₂O and SiO₂) was melted at 1600°C and 7.7 GPa before quenching. A reference LS₂ glass sample was produced at atmospheric pressure using conventional melting and quenching procedure. The samples were characterized by X-ray diffraction, differential thermal analysis, and instrumented ultramicro hardness measurements. X-ray diffraction confirmed that all samples were amorphous and thermal analysis suggests that different glassy structures were produced depending on the route of synthesis. Hardness and elastic modulus of the glasses produced under high pressure were higher than those of the reference glass, reflecting the irreversible densification effect induced by the high-pressure processing.     

Low-Field Nuclear Magnetic Resonance Time Domain Characterization of Polyunsaturated Fatty Acid–Rich Linseed and Fish Oil Emulsions during Thermal Air Oxidation

Linseed contains high levels of polyunsaturated fatty acids (PUFA), such as α-linolenic acid (> 50% ALA-18:3), that are naturally protected against thermal oxidation by their encapsulation within linseed oil bodies (OB) by multiple components including antioxidant proteins and mucilage emulsifying agents. Linseed OB emulsions (LSE) can be produced by grinding linseed seeds, adding water, adjusting pH, and sonication. This is a process that can encapsulate externally added PUFA to minimize their thermal oxidation, as it does for the intrinsic ALA PUFA. Fish oil (FO) encapsulation into this LSE platform to form linseed fish oil emulsions (LSFE) offers the possibility of a nutritive delivery system of the biologically essential FO PUFA eicosapentaenoic acid and docosahexaenoic acid. In this study, ¹H low-field nuclear magnetic resonance (LF-NMR) is used to characterize LSE's and LSFE's chemical and structural properties as well as their stability and changes under thermal oxidation (55 °C for 96 hours). ¹H LF-NMR data processing was developed to generate one-dimensional (1D) T₁ (spin–lattice), 1D T₂ (spin–spin), and 2D (T₁ vs. T₂) relaxation time spectra that can characterize OB emulsions and monitor their time domain fingerprints (spectrum peaks) of chemical and structural changes during the oxidation process. The ¹H LF-NMR analysis were further supported and correlated with conventional peroxide value test, self-diffusion, droplet size distribution, zeta potential estimation of surface stability, and gas chromatography–mass spectrometry analysis of fatty acid profile changes under thermal oxidation conditions. The 1D and 2D LF-NMR relaxation spectra showed that the LSE and LSFE did not suffer intense oxidation process, due to PUFA assembly in OB oxidative protection. These results were further confirmed by the supportive analytical methodologies. The results of this study demonstrate the efficacy of ¹H LF-NMR methodology to monitor PUFA's rich oil and emulsion thermal oxidation.     

A biased random‐key genetic algorithm for OSPF and DEFT routing to minimize network congestion

Interior gateway routing protocols like Open Shortest Path First (OSPF) and Distributed Exponentially Weighted Flow Splitting (DEFT) send flow through forward links toward the destination node. OSPF routes only on shortest‐weight paths, whereas DEFT sends flow on all forward links, but with an exponential penalty on longer paths. Finding suitable weights for these protocols is known as the weight setting problem (WSP). In this paper, we present a biased random‐key genetic algorithm for WSP using both protocols. The algorithm uses dynamic flow and dynamic shortest path computations. We report computational experiments that show that DEFT achieves less network congestion when compared with OSPF, while, however, yielding larger delays.     

Correspondence of projected 3‐D points and lines using a continuous GRASP

The field of computer vision has experienced rapid growth over the past 50 years. Many computer vision problems have been solved using theory and ideas from algebraic projective geometry. In this paper, we look at a previously unsolved problem from object recognition, namely object recognition when the correspondences between the object and image data are not known a priori. We formulate this problem as a mixed‐integer non‐linear optimization problem in terms of the unknown projection relating the object and image, as well as the unknown assignments of object points and lines to those in the image. The global optimum of this problem recovers the relationship between the object points and lines with those in the image. When certain assumptions are enforced on the allowable projections mapping the object into the image, a proof is provided which permits one to solve the optimization problem via a simple decomposition. We illustrate this decomposition approach on some example scenarios.     

Characterization of Crude and Partially Purified Lipase from Geotrichum candidum Obtained with Different Nitrogen Sources

Lipases from Geotrichum candidum were produced in two different medium: A = 12 % (w/v) clarified corn steep liquor (CCSL) + 0.6 % (w/v) soybean oil (SO) and B = 3.5 % (w/v) yeast hydrolysate (YH) + 0.7 % (w/v) SO. Lipases were partially purified from both media by hydrophobic interaction chromatography using 3.0 mol L^?1 of NaCl as mobile phase, and they were characterized in the crude and partially purified forms. The recovery of lipase activity from CCSL and YH via HIC were 96 and 94.3 %, and the purification factors were 44.3 and 86.7‐fold, respectively. All evaluated lipases had similar optimum pH (7.0–7.7), but, for the CCSL crude lipase, optimum temperature (47 °C) was 10 °C higher than others lipases evaluated. CCSL crude lipase possessed a higher thermo stability than YH crude lipase, e.g., at 37 °C (pH 7.0) the half‐life of CCSL crude lipase was 19.25 h and at pH 8.0 (30 °C) the half‐life was 48 h, which are five and ten times higher than with YH crude lipase, respectively. On the other hand, the YH crude lipase possessed a higher catalytic constant (k_cat = 2.3 min^?1) but with almost the same catalytic efficiency (K_m/k_cat = 32.12 mg mL min^?1) in relation to CCSL crude lipase. The lipases differ in biocatalytic properties between substrates, suggesting that the two lipases can be employed for different applications.     

Alkyl Tail Segments Mobility as a Marker for Omega-3 Polyunsaturated Fatty Acid-Rich Linseed Oil Oxidative Aging

Omega-3 polyunsaturated fatty acid (PUFA)-rich linseed oil (LSO) is an important component in biological systems, foods, and many other industrial products. In recent years, LSO has attracted increased attention in the field of functional foods, which has highlighted its facile susceptibility to aging by autoxidation. Common colorimetric and a long list of spectral methodologies have been used to follow after and predict LSO shelf life's quality, especially in regards to aging by autoxidation. These standard methodologies are nevertheless limited, because of the complexity of the LSO's chemical and physical changes. The goal of the present study is to develop a sensorial ¹H LF-NMR energy relaxation time application based on monitoring primary chemical and structural changes occurring with time and temperature during oxidative thermal stress for better and rapid evaluation of LSO's aging process. Using ¹H low-field NMR, the different T₂ times of energy relaxations due to spin–spin coupling, and proton motion/mobility of LSO molecular segments were monitored. As previously reported, we characterized the chemical and structural changes in all phases of the autoxidation aging process. Starting from the initiation phase (abstraction of hydrogen radical, fatty acid chain rearrangement, and oxygen uptake yielding hydroperoxides products), through to the propagation phase (chain reactions resulting in tail cleavage to form alkoxy radicals, and alpha, beta-unsaturated aldehydes formation), and a termination phase (cross linking and production of polymerization end products). The ¹H LF NMR transverse relaxation approach, monitors both the covalent bond's strong forces (100–400 kJ mol⁻¹) in LSO oxidative aging decomposition, as well as secondary relatively weak interactive forces by hydrogen bonds (~70 kJ mol⁻¹), and electrostatic bonds (0–50 kJ mol⁻¹) contributing to secondary crosslinking interactions leading to a LSO viscous gel of polymerized products in the termination phase. In the present paper, we show that LSO tail segments mobility in terms of T₂ multi-exponential energy relaxation time decays, generated by data reconstruction of ¹H transverse relaxation components are providing a clear, sharp, and informative understanding of LSO sample's autoxidation aging processes. To support T₂ time domain data analysis, we used data from high-field band-selective ¹H NMR pulse excitation for quantification of hydroperoxides and aldehydes of the same LSO samples treated under the same thermal conditions (25, 40, 60, 80, 100, 120 °C) with pumped air for 168 hours. Peroxide value, viscosity, and self-diffusion analyses, as well as fatty acids profile and by-products determined by GC–MS on the same samples were carried out, and correlated with the LSO tail T₂ energy relaxation time results. From these results, it is postulated that selective determination of LSO tail T₂ time domain can be used as a rapid evaluation marker for following omega-3 PUFA-rich oils oxidative aging process within industrial and commercial products.     

A random key based genetic algorithm for the resource constrained project scheduling problem

This paper presents a genetic algorithm for the Resource Constrained Project Scheduling Problem (RCPSP). The chromosome representation of the problem is based on random keys. The schedule is constructed using a heuristic priority rule in which the priorities of the activities are defined by the genetic algorithm. The heuristic generates parameterized active schedules. The approach was tested on a set of standard problems taken from the literature and compared with other approaches. The computational results validate the effectiveness of the proposed algorithm.     

A flux observer for induction machines based on a time-variantdiscrete model

An alternative approach to obtaining a discrete-time counterpart to the two-axis continuous model of an induction machine is presented. The discrete time-variant equations are derived from a partial discretization of the continuous state equation. The discrete model can be used with advantage in simulation and real-time control applications. A discrete time-variant reduced-order flux observer based on the discrete model is proposed. Computer simulation results are shown to compare the proposed discrete model with that obtained from the Euler method and the exact continuous model