A study on the effect of the asymmetry on real capacitated vehicle routing problems

Matrices with distances between pairs of locations are essential for solving vehicle routing problems like the Capacitated Vehicle Routing Problem (CVRP), Traveling Salesman Problem (TSP) and others. This work deals with the complex reality of transportation networks and asymmetry. Through a series of comprehensive and thorough computational and statistical experiments we study the effect that many factors like asymmetry, geographical location of the depot and clients, demand, territory and maximum vehicle capacity have in the solution of CVRP instances. We examine both classical heuristics as well as current state-of-the-art metaheuristics and show that these methods are seriously affected by the studied factors from a solution time and quality of solutions perspective. We systematically compare the solutions obtained in the symmetric scenario with those obtained in the real asymmetric case at a quantitative as well as a qualitative level, with the objective of carefully measuring and understanding the differences between both cases.     

Comprehensive characterization of the functional activities of pressurized liquid and ultrasound-assisted extracts from Chlorella vulgaris

Chlorella vulgaris has been referred as a potential source of bioactive compounds (carotenoids and fatty acids). In this work, the ability of an environmentally friendly extraction technique such as Pressurized Liquid Extraction (PLE) and a traditional extraction technique such as Ultrasound-Assisted Extraction (UAE) to obtain functional compounds from C. vulgaris, at analytical scale, has been demonstrated. Seeked bioactivities were antioxidant and antimicrobial, for their interest in the food industry. Therefore, a methodology including analytical extraction, in-vitro assays and chemical characterization via HPLC-DAD and GC–MS has been used to determine the interest of Chlorella as a source of functional food ingredients. Results demonstrated that PLE provide higher yields than UAE while similar bioactivities were obtained. Important concentration of carotenoids (lutein, neoxanthin, β-carotene, etc.), chlorophylls, sterols, phytols, and fatty acids (among others) have been found in Chlorella extracts that could be correlated to the observed biological activity.     

Online Scheduling FIFO Policies with Admission and Push-Out

We consider the problem of managing a bounded size First-In-First-Out (FIFO) queue buffer, where each incoming unit-sized packet requires several rounds of processing before it can be transmitted out. Our objective is to maximize the total number of successfully transmitted packets. We consider both push-out (when a policy is permitted to drop already admitted packets) and non-push-out cases. We provide worst-case guarantees for the throughput performance of our algorithms, proving both lower and upper bounds on their competitive ratio against the optimal algorithm, and conduct a comprehensive simulation study that experimentally validates predicted theoretical behavior.     

Development of a novel device for applying uniform doses of electron beam irradiation on carcasses

The Maxim's Electron Scatter Chamber (Maxim Chamber) was developed to obtain uniform dose distribution when applying electron beam (e-beam) irradiation to materials of irregular surface. This was achieved by placing a stainless steel mesh surrounding a cylindrical area where the target sample was placed. Upon contact with the mesh, electrons scatter and are directed onto the target from multiple angles, eliminating the e-beam linearity and resulting in a uniform dose distribution over the target surface. The effect of irradiation in the Maxim Chamber on dose distribution and pathogen reduction was tested on rabbit carcasses to simulate other larger carcasses. The dose uniformity ratio (DUR) on the rabbit carcasses was 1.8, indicating an acceptable dose distribution. On inoculated carcasses, this treatment reduced Escherichia coli O157:H7 by > 5 log cycles. These results indicate that carcass irradiation using e-beam is feasible using the Maxim's electron scattering chamber. Appropriate adjustments will be further needed for commercial application on beef and other animal carcasses.     

Anisotropic diffusion of hydrogen in nanoporous carbons

It is accepted that hydrogen transport capacity through carbons depends on the anisotropy of the empty spaces that constitute their porous structure. However, very little is known about this relationship. Computational simulation is an excellent tool to accomplish this kind of studies. Simulation requires digital representations of materials and a model describing the interaction potential among the gas molecules and the solids surfaces. In this work, it is proposed to use the analytical solutions of the truncated pore problem for modeling the potentials, and an immiscible lattice gas for obtaining the representations. The degree of anisotropy was quantified by using the mean intercept length method. The adsorption isotherms and the self-diffusion coefficients in the three orthogonal directions were found by the grand canonical and kinetic Monte Carlo methods, respectively. The results suggest the existence of a gas pressure at which a molecular saturation threshold (P _s) is reached. P _s determines if the degree of anisotropy is or not a representative variable of diffusive transport. For P ≤ P _s, the degree of anisotropy favors the molecular mobility. When P > P _s, the degree of anisotropy loses influence on mobility.     

An adaptive color similarity function suitable for image segmentation and its numerical evaluation

In this article, we present an adaptive color similarity function defined in a modified hue‐saturation‐intensity color space, which can be used directly as a metric to obtain pixel‐wise segmentation of color images among other applications. The color information of every pixel is integrated as a unit by an adaptive similarity function thus avoiding color information scattering. As a direct application we present an efficient interactive, supervised color segmentation method with linear complexity respect to the number of pixels of the input image. The process has three steps: (1) Manual selection of few pixels in a sample of the color to be segmented. (2) Automatic generation of the so called color similarity image (CSI), which is a gray level image with all the gray level tonalities associated with the selected color. (3) Automatic threshold of the CSI to obtain the final segmentation. The proposed technique is direct, simple and computationally inexpensive. The evaluation of the efficiency of the color segmentation method is presented showing good performance in all cases of study. A comparative study is made between the behavior of the proposed method and two comparable segmentation techniques in color images using (1) the Euclidean metric of the a* and b* color channels rejecting L* and (2) a probabilistic approach on a* and b* in the CIE L*a*b* color space. Our testing system can be used either to explore the behavior of a similarity function (or metric) in different color spaces or to explore different metrics (or similarity functions) in the same color space. It was obtained from the results that the color parameters a* and b* are not independent of the luminance parameter L* as one might initially assume in the CIE L*a*b* color space. We show that our solution improves the quality of the proposed color segmentation technique and its quick result is significant with respect to other solutions found in the literature. The method also gives a good performance in low chromaticity, gray level and low contrast images. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 156–172, 2017     

Effect of rheology and humic acids on the transport of environmental fluids: Potential implications for soil remediation revealed through microfluidics

This study investigated the potential effect of shear rheology and humic acids (HA) on the subsurface transport of polymeric fluids used for the remediation of contaminants. Polymeric fluids were prepared with guar, scleroglucan, and carboxymethyl cellulose (CMC). Guar fluids can be used to suspend reactive particles for contaminant degradation. Fluids prepared with 2.5 g/L of guar in water were viscous, and the crosslinker borax (1 g/L) made them viscoelastic. Microfluidics experiments showed that the increase in elasticity blocked the flow of guar in 350 μm channels. Guar, CMC, or scleroglucan fluids containing sodium thiosulfate can be used to trap toxic Cr(VI) in the subsurface and reduce it to harmless Cr(III). Trapping of Cr(VI) is achieved by the gelation of the fluids upon contact with chromium. Before mixing with chromium, HA did not affect the flow of CMC, guar, and scleroglucan in microfluidic channels. Quartz-crystal microbalance with dissipation monitoring experiments indicates that HA reduced sorption of guar onto silica, potentially promoting the transport of guar fluids in sandy aquifers. While HA slightly decreased the rate of gelation of CMC and scleroglucan upon contact with chromium, it did not affect the fast gelation rate of guar. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48465.