Energy Criticality Avoidance-Based Delay Minimization Ant Colony Algorithm for Task Assignment in Mobile-Server-Assisted Mobile Edge Computing.

Mobile edge computing has been an important computing paradigm for providing delay-sensitive and computation-intensive services to mobile users. In this paper, we study the problem of the joint optimization of task assignment and energy management in a mobile-server-assisted edge computing network, where mobile servers can provide assisted task offloading services on behalf of the fixed servers at the network edge. The design objective is to minimize the system delay. As far as we know, our paper presents the first work that improves the quality of service of the whole system from a long-term aspect by prolonging the operational time of assisted mobile servers. We formulate the system delay minimization problem as a mixed-integer programming (MIP) problem. Due to the NP-hardness of this problem, we propose a dynamic energy criticality avoidance-based delay minimization ant colony algorithm (EACO), which strives for a balance between delay minimization for offloaded tasks and operational time maximization for mobile servers. We present a detailed algorithm design and deduce its computational complexity. We conduct extensive simulations, and the results demonstrate the high performance of the proposed algorithm compared to the benchmark algorithms.

Enhanced Microwave-Absorbing Property of Honeycomb Sandwich Structure with a Significant Interface Effect.

Honeycomb sandwich structures (HSSs) are excellent candidates for light and efficient microwave-absorbing materials. In this work, we design an HSS using SiO2 fiber-reinforced epoxy resin (SiO2f/ER) composites as both the top and bottom layers to improve the impedance matching with free space. Target dielectric properties of the honeycomb and coated lossy material of the HSS were calculated based on the multilayer transmission line theory, metal backplane model, and homogenization theory. In addition, the interface effect between the SiO2f/ER and honeycomb of the HSS was discussed theoretically, experimentally, and numerically, indicating a 1-4% contribution of microwave absorption resulting from the interface. By analyzing the equivalent resistance, equivalent capacitance, as well as equivalent inductance, the enhanced microwave absorption of HSS is attributed to the formation of the interfacial transition zone, which benefits both impedance matching and electromagnetic loss.

Effect of low molecular weight organic acids on adsorption and desorption of fluoride on variable charge soils.

The effect of four low molecular weight organic acids on F(-) adsorption by two variable charge soils was investigated using a batch method. The organic acids reduced F(-) adsorption through competition by the acids with F(-) for sorption sites. Oxalic and malonic acids, both of which have simpler chemical structures, were more effective than citric or malic acid. The effect of organic acids on F(-) adsorption was more prominent at higher pH values and with larger amounts of the organic acids. The desorption study showed that the organic acids enhanced the desorption of F(-) adsorbed by the soils. In the control and malic acid systems, desorption increased sharply with decreasing pH, while in the oxalic acid system, desorption rose slightly with decreasing pH. Desorption also increased with increasing amount of organic acid added. There are two possible mechanisms for the effect of the organic acids on F(-) adsorption and desorption: (1) competition of the organic acids with F(-) for adsorption sites and (2) dissolution of the adsorbents, especially dissolution of soil Al.

Effect of low-molecular-weight organic anions on exchangeable aluminum capacity of variable charge soils.

Low-molecular-weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes, such as nutrient availability, translocation of metals, fate of heavy metals, and mineral weathering. In this paper, the effect of the LMW organic anions on the exchangeable aluminum of two variable-charge soils was examined. The results showed that the organic anions induced an increase or a decrease in the exchangeable Al, and the extent and direction of the effect depended on the nature of organic anions, surface chemical properties of soils, and pH. For example, at pH 4.5, the quantity of exchangeable Al of Oxisol in the control system was 2.65 mmol kg(-1), whereas the values in the citrate, oxalate, malonate, malate, tartarate, salicylate, and lactate systems increased by 3.25, 1.93, 1.95, 1.82, 1.28, 0.88, and 0.45 times, respectively. In contrast, the quantity of the exchangeable Al of Ultisol at pH 4.5 in the oxalate and the citrate systems decreased by 8.8 and 19.6%, respectively. The increase in the exchangeable Al was caused mainly by the increase in negative surface charge of the soils due to the specific adsorption of organic anions. The ability of organic anions at low concentrations to increase exchangeable Al for Oxisol followed the order citrate > oxalate and malonate > malate > tartarate > salicylate > maleate > lactate. This order is consistent with that of the effect of the adsorption of anions on the increase in the negative surface charge and/or the decrease in the positive surface charge of the soil. On the other hand, the organic anions could depress the exchangeable Al through the formation of soluble Al-organic anion complexes under certain conditions. The anions with small stability constants of Al-organic anion complexes, such as lactate, caused an increase in exchangeable Al with the change in surface charge of the soils, while those with large stability constants, such as citrate and oxalate, caused an increase in the exchangeable Al at low concentration and a decrease at high concentration.

Effect of Cr(VI) anions on adsorption and desorption behavior of Cu(II) in the colloidal systems of two authentic variable charge soils.

Heavy metals in wastes exist as multiple pollutants. The study of the interactions between multiple pollutants and soils should be of significance in practice. In the present study, the effect of chromate on adsorption and desorption behavior of Cu(II) in two variable charge soils was investigated, with the emphasis on the adsorption and desorption equilibria of Cu(II). The results showed that chromate can affect adsorption and desorption of Cu(II) in the colloidal systems of two variable charge soils. The extent of the effect was related to the initial concentrations of chromate and Cu(II), the system pH, and the nature of the soils. The presence of chromate led to an increase in the adsorption of Cu(II). For example, in the presence of 0.5, 0.8, 1.0, and 1.5 mmol L(-1) of chromate, for the rhodic ferralsol the adsorption of Cu(II) increased by 15.3, 18.0, 19.0, and 20.2%, respectively. For the hyperrhodic ferrasol, the corresponding figures were 11.9, 17.0, 20.3, and 26.1%, respectively. The presence of chromate also caused an increase in the desorption of Cu(II). For instance, in the presence of 0.5, 1.0, and 1.5 mmol L(-1) of chromate, the desorption for the rhodic ferralsol increased by 16.9, 27.5, and 34.1%, respectively. For the hyperrhodic ferralsol, the corresponding figures were 18.1, 35.6, and 51.4%, respectively. The increments of the adsorption and desorption increased with the increase in equilibrium concentration of Cu(II) in the solution. For instance, when the equilibrium concentrations were 0.5, 1.0, 1.5, and 2.0 mmol L(-1), the increments for the rhodic ferralsol were 2.5, 3.2, 3.3, and 3.0 mmol kg(-1), respectively. For the hyperrhodic ferralsol, the corresponding figures were 2.9, 3.5, 4.0, and 4.2 mmol kg(-1), respectively. The effect of chromate for the hyperrhodic ferralsol was greater than that for the rhodic ferralsol. This is caused by the difference in the content of iron oxides for the two soils. The increments of the adsorption and the desorption of Cu(II) increased with the rise in pH, reaching a maximum value, and then decreased. It can be assumed that the increment of the adsorption was caused by the change in surface charge of the soils induced by the adsorption of chromate and the cooperative adsorption of chromate adsorbed and Cu(II). The increase of electrostatically adsorbed Cu(II) was responsible for the increase in the desorption of Cu(II).

Effect of low-molecular-weight organic anions on electrokinetic properties of variable charge soils.

It is known that some inorganic anions can be adsorbed by variable-charge soils specifically, resulting in the lowering of the zeta potential of the clay particle. Reasoning similarly, organic anions should also have such an effect. In this article, the effect of the anions of five low-molecular-weight (LMW) organic acids existing widely in soils on the zeta potentials of two variable-charge soils was examined. The results showed that the presence of organic anions led to a decrease in zeta potential. The effect of different anions on zeta potential followed the order oxalate>citrate>malate>maleate>acetate. The effect increased with the increase in anion concentration and decreased with the increase in pH. The extent of the effect on different soils was apparently related to their iron oxide content. The presence of organic anions also led to a decrease in the isoelectric point (IEP) of the soil. The IEPs of two soils in organic anion systems followed the order acetate>maleate>malate>citrate. No IEP was detected for the oxalate system.

Interactions between variable-charge soils and acidic solutions containing fluoride: an investigation using repetitive extractions.

The reaction between two variable-charge soils and acidic solutions containing F was investigated with a repetitive extraction method. When added F concentration was 10(-4) mol/L, F did not markedly enhance solution pH in the whole prolonged extractions, in comparison with F-free acidic solution extractions. Most of the added F was adsorbed on soil surfaces and Al-F complexes were the dominant F species in solution. With increasing extractions, the fraction of Al-F slightly increased, arising from dissolution and/or desorption of Al. In comparison with F-free acidic solution extractions, F-induced Al dissolution did not significantly increase Al release, probably because of the modest reactivity of metal-F surface complexes at terminal sites at low F loading. The gradual decrease in Al release in the following extractions was due to the gradual depletion of readily reactive Al-containing mineral phases. In contrast to the low F loading, at an F concentration of 10(-3) mol/L, the pH was enhanced dramatically in the initial extraction and a high pH was maintained in the following extractions. In the initial extraction, the increase in negative surface charges and solution pH seemingly depressed proton-induced Al dissolution and enhanced readsorption of some positively charged Al-F complexes, resulting in low amounts of Al and F in solution. In the following several extractions, F-induced Al dissolution and desorption of Al-F complexes substantially enhanced the amounts of Al and F, and the fraction of Al-F complexes in solution. Several interconnected mechanisms such as ligand exchange, the release of OH(-) ions from soluble hydroxylated Al groups, desorption of Al as Al-F complexes, and F-induced breakdown of soil minerals were responsible for the alteration in pH, Al release, and the fraction of Al-F complexes in the later extractions. A molecular-level interpretation is needed in order to address the different impacts of varying F concentration levels on soil chemistry and environments.

Effect of low-molecular-weight organic anions on surface charge of variable charge soils.

Low-molecular-weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes. In the present paper, the effect of the anions of four low-molecular-weight organic acids on the surface charge of three variable charge soils was investigated. The results showed that the presence of organic anions led to an increase in negative charge and a decrease in positive charge. Positive charges decreased to a larger extent than negative charges. The effect of different anions on surface charge followed the order citrate > malate > oxalate > acetate. For hyper-rhodic ferrasol and rhodic ferrasol, the change of positive charge decreased with the increase in pH, while that of negative charge increased with the increase in pH. Among different soils the extent of change in surface charge was related to their iron oxides content. When free iron oxides were removed from the soil, the effect of organic anions on surface charge decreased sharply. These findings may be of practical significance for variable charge soils low in nutrient-retaining capacity by increasing the retaining capacity for cations such as potassium and calcium considerably but decreasing that for anions such as nitrate remarkably.

Determination of strongly reducing substances in sediment.

Reducing substances in sediments play an important role in regulating the chemical and biological status of the sediment. Strongly reducing substances are the most active part of them, and are difficult to measure directly. In this work, we have developed a method for their determination based on the oxidation by Fe(III). Then, the produced Fe(II) was determined by colorimetry, using 2,2'-bipyridine as the chelating agent. Prior to determination, these substances were extracted from the sediment by M acetic acid. The whole process was carried out in a closed system, so that oxidation of Fe(II) and reducing substances by atmospheric oxygen could be avoided. The calibration curve between absorbance and Fe(II)-chelate concentration in extract was linear. When ascorbic acid was added to the extract, the recovery was larger than 94.0%. The effect of surplus Fe(III) on the result was discussed. With the proposed method, the concentration of strongly reducing substances in sediment samples from Dianchi Lake of China was measured with good reproducibility.