301 research outputs found
Electroplating of non-fluorinated superhydrophobic Ni/WC/WS<sub>2</sub> composite coatings with high abrasive resistance
No full textWeak hierarchical rough structures on superhydrophobic surfaces hinder their practical industrial applications. This paper reports a strategy to fabricate robust nickel-based superhydrophobic coatings via the codeposition of nanosized WS2 and WC particles. The Ni/WC/WS2 composite coatings were synthesized on mild steel substrates by one-pot electroplating followed by the adsorption of stearic acid self-assembled monolayers to modify the surface wetting. The particle concentration in the bath was investigated and the maximum water contact angle of approx. 170° was achieved by optimizing the particle contained. Hardened by WC and lubricated by WS2 inclusions the superhydrophobic coatings showed remarkable abrasive resistance with a bearing capacity ≥10,000 mm abrasion length. The coatings also showed aerophilic behavior and good environmental stability over >6 months
Hydrogen Production During the Dark Fermentation of Glycerol
No full textThe focus of this thesis was on the production of H2 from glycerol by mixed anaerobic cultures through dark fermentation. Laboratory scale experiments were conducted to demonstrate H2 production from glycerol. The impact of various factors was evaluated using different analytical and statistical methods. Three pH levels (5.5, 6.5, and 7.5) were examined to determine the effects of the initial pH on H2 production from glycerol. A hydrogen yield of 0.33 ± 0.03 mol H2 mol–1 glycerol was observed in cultures with the initial pH set at 5.5. Further experiments were focused on increasing the H2 yield using long chain fatty acids (LCFAs) as inhibitors together with glycerol in mixed anaerobic cultures with an initial pH of 5.5. Six LCFAs including lauric acid (LUA), myristic acid (MA), palmitic acid (PA), stearic acid (SA), oleic (OA), and linoleic acid (LA) were examined in this study. Higher H2 yields were observed in cultures fed PA, OA, or LA when compared to cultures fed with only glycerol. The H2 yield for the OA and LA treated cultures were 0.42 ± 0.01 and 0.46 ± 0.03 mol H2 mol–1 glycerol, respectively. In the LA and glycerol fed cultures, the H2 yield was 29% larger when compared to the glycerol control. Based on the electron balance, ethanol (EtOH) (approximately 23.1% of the total electron equivalents) and 1,3-propanediol (1,3 PDO) (approximately 50.0% of the total electron equivalents) were the major metabolites in the LA treated cultures, while approximately 6.5% and 7.9% electron equivalents were directed to H2 and acetate (Ac-) formation, respectively. A three-factor and three-level BBD model was conducted to maximize the H2 yield in cultures fed glycerol and LA. The initial pH levels (5.5, 6.5, 7.5), glycerol concentrations (1,300, 2,600, 5,110 mg L–1), and operational temperatures (22, 37, 52 °C) were three factors selected in this study. The highest H2 yield was 0.86 ± 0.02 mol H2 mol–1 glycerol at 55 °C, a pH of 5.5, and a glycerol concentration of 2,600 mg L–1. The predicted result was 0.84 mol H2 mol–1 glycerol at 55 °C, a pH of 5.5, and a glycerol concentration of 2,710 mg L–1 using the D-optimality analysis. Based on the designed BBD model, the optimum levels of three factors were significant when predicting the highest H2 yield by the D-optimality analysis
Clean energy: Hydrogen production from glycerol via dark fermentation
No full textSustainable IndustryThe demand for renewable and clean energy supplies is increasing because of depleting fossil fuels and global warming. Hydrogen (H2) is the only carbon-free energy source which is regarded as the cleanest fuel since water is the only product during combustion. Bio-hydrogen (bio-H2) production is promising because many organic wastes can be utilized as feedstocks. Bacteria fermentation, a similar process taking place during food digestion in our gut system, can be utilized to produce bio-H2. Glycerol, a waste byproduct from the manufacture of biodiesel, is a low-value chemical that can be converted intoH2. Biodiesel is a transportation fuel produced which is from algae. Converting glycerol intoH2 could be an economic advantage for many biodiesel industries. Adding fatty acids which are produced from oils such a safflower and sunflower oils can improve H2 production from glycerol during bacterial fermentation. Although bio-H2 production from glycerol through dark fermentation by using selected bacterium has been reported, the performance of H2 yield needs to be analyzed when mixed bacteria and H2-improving treatment are conducted. The main objective of this work was to establish a maximumH2 yield during the glycerol fermentation in the mixed cultures with the presence of fatty acids
On Homogeneous Parameter-Dependent Quadratic Lyapunov Function for Robust H∞ Filtering Design in Switched Linear Discrete-Time Systems with Polytopic Uncertainties
No full textThis paper is concerned with the problem of robust H∞ filter design for switched linear discrete-time systems with polytopic uncertainties. The condition of being robustly asymptotically stable for uncertain switched system and less conservative H∞ noise-attenuation level bounds are obtained by homogeneous parameter-dependent quadratic Lyapunov function. Moreover, a more feasible and effective method against the variations of uncertain parameter robust switched linear filter is designed under the given arbitrary switching signal. Lastly, simulation results are used to illustrate the effectiveness of our method
A hybrid grid-based method for mining arbitrary regions-of-interest from trajectories
No full textThere is an increasing need for a trajectory pattern mining as the volume of available trajectory data grows at an unprecedented rate with the aid of mobile sensing. Region-of-interest mining identifies interesting hot spots that reveal trajectory concentrations. This article introduces an efficient and effective grid-based region-of-interest mining method that is linear to the number of grid cells, and is able to detect arbitrary shapes of regions-of-interest. The proposed algorithm is robust and applicable to continuous and discrete trajectories, and relatively insensitive to parameter values. Experiments show promising results which demonstrate benefits of the proposed algorithm
Multi-surrogate multi-tasking optimization of expensive problems
No full textLiao P, Sun C, Zhang G, Jin Y. Multi-surrogate multi-tasking optimization of expensive problems. Knowledge-Based Systems. 2020;205: 106262.Multiple surrogates can be trained in surrogate-assisted optimization of expensive problems to describe different characteristics of the real fitness landscape. It has been shown that optimization assisted by multiple surrogate models are beneficial compared to a single surrogate. Along this line of research, we propose to train two surrogate models, one global surrogate model trained using all available data, and the other one local surrogate model trained using only part of the data subsequently selected from the data sorted according to an ascending order of the objective value. Different from most existing multi-surrogate based approaches, however, we adopt the multi-tasking optimization framework to accelerate the convergence by regarding the two surrogates as two related tasks. This way, two optimal solutions found by the multi-tasking algorithm will be evaluated using the real expensive objective function, and consequently, both the global and local models will be updated. This process repeats until the allowed computational budget is exhausted. Experiments are conducted on twelve widely used benchmark problems of up to 200 dimensions to examine the performance of the proposed algorithm. Our results show that the proposed method is very competitive, has quick convergence and scales well with the increase in the number of decision variables for solving computationally expensive single-objective optimization problems
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