Marangoni Propulsion of Active Particles

We study the surfing motion of active particles located at a flat liquid-gas interface. The particles create and maintain a surface tension gradient by asymmetrically discharging a surface tension-reducing agent. We employ theory and numerical simulation to investigate the Marangoni propulsion of these active surfers. First, we use the reciprocal theorem to establish a relationship between the propulsion speed and the release of the active chemical. This theoretical relation is utilized to examine the effect of wall confinement and geometry on the Marangoni-driven motion of active particle when the inertial effects are negligible and when the transports of the released agent is dominated by diffusion. Contrary to what might be the usual expectation, we find that the surfers may propel in the lower surface tension direction depending on their geometry and proximity to the bottom of the liquid layer. We then extend our theory beyond the Stokes regime with the aid of the perturbation theory and calculate the leading-order corrections to the propulsion speed due to the advective transport of momentum and mass when (Re, Pe) (denoted by Re and Pe, respectively) are small, but finite. Next, we develop a computational framework that enables us to study the effects of intermediate and large Re and Pe on the propulsion speed. Our numerical approach is validated against theory and available experimental data. Interestingly, our simulations reveal that the normalized propulsion speed initially increases with increasing Re and Pe from zero. It then reaches a maximum and afterward sharply declines when Re or Pe becomes large. That there exist certain intermediate (Re, Pe) at which the Marangoni propulsion reaches a peak is a new discovery that can guide engineering to design Marangoni surfers with superior performance. We also numerically analyze the translational stability of Marangoni surfers of spherical shape. An overset-grid is adopted to carry out the simulations. We demonstrate that a Marangoni surfer can retain its stability at higher Reynolds numbers relative to the same surfer moving at an interface with no Marangoni effect present. Lastly, we computationally investigate the change in the mobility of the surfers as a result of the depth of the liquid layer. We consider the motion of thin cylindrical disks and oblate spheroids for a wide range of release rates and diffusivity of the exuded chemical species, that control the effective (Re, Pe). We show that indeed the surfers can undergo a forward, a backward, or an arrested motion. We also identify the links between these modes of mobility and the forces acting on the surfers as well as the flow structure in their vicinity. Rather unexpectedly, we discover that negative pressure is the primary contributor to the fluid force experienced by the surfer and that this suction force is mainly responsible for the reverse Marangoni propulsion. Overall, our findings substantially improve the current understanding of the Marangoni-driven motion of active particles at liquid-gas interfaces and pave the way for engineering future miniature surfing robots

Enhanced Anaerobic Digestion of Organic Waste

Anaerobic digestion (AD) of organic municipal solid waste (OMSW) is considered as a key element in sustainable municipal waste management due to its benefits for energy, environment, and economy. This process reduces emission of greenhouse gases, generates renewable natural gas, and produces fertilizers and soil amendments. Due to its advantages over other treatment methods and waste-to-energy technologies, anaerobic digestion has attracted more attention so that numerous research works in this area are performed. In this chapter, an overview of previous studies on anaerobic digestion using OMSW as the feedstock is presented. First, the principals of anaerobic digestion including chemical and biological pathways and microorganisms responsible for different steps of the process are discussed. Factors influencing the efficiency of the process such as temperature, pH, moisture content, retention time, organic loading rate and C/N ratio are also presented in this chapter. Different methods of pretreatment applied to enhance biogas production from anaerobic digestion of municipal solid waste are also discussed

Removal of Cationic Surfactants from Aqueous Solutions by Modified Cotton as a Novel High Capacity and Low Cost Adsorbent

Direct and indirect releases of large quantities of surfactants to the environment may result in serious health and environmental problems. Therefore, surfactants should be removed from water before release to the environment or delivery for public use. Using cotton-based adsorbent may be an effective technique to remove surfactants. In this study, the removal of cationic surfactants by modified cotton was investigated. N-Cetyl-N,N,N-trimethylammonium bromide (CTAB) was selected as a cationic surfactant for the experiments. The results revealed that the modified cotton has a high affinity toward the cationic surfactants. Experiments were conducted to examine the effects of applied adsorbent dosage, initial concentration of adsorbate, pH, temperature, salt concentration on the removal efficiency. By increasing the salt concentration, removal efficiency was decreased slightly. The temperature had an adverse effect on removal efficiency. The adsorption of the CTAB increases with increasing pH of the solution. A series of batch experiments were performed to determine the sorption isotherms of modified cotton. Surfactant equilibrium data fitted very well to the Langmuir model. The Langmuir model showed that the maximum adsorption was 909 mg/g which is higher than the capacity of other adsorbents reported until now. The pseudo first-, second- order and corresponding rate equation kinetic models were investigated. Adsorption complies with a pseudo-second-order rate equation

Free-Decay Heave Motion of a Spherical Buoy

We examined the heave motion of a spherical buoy during a free-decay drop test. A comprehensive approach was adopted to study the oscillations of the buoy involving experimental measurements and complementary numerical simulations. The experiments were performed in a wave tank equipped with an array of high-speed motion-capture cameras and a set of high-precision wave gauges. The simulations included three sets of calculations with varying levels of sophistication. Specifically, in one set, the volume-of-fluid (VOF) method was used to solve the incompressible, two-phase, Navier–Stokes equations on an overset grid, whereas the calculations in other sets were based on Cummins and mass-spring-damper models that are both rooted in the linear potential flow theory. Excellent agreements were observed between the experimental data and the results of VOF simulations. Although less accurate, the predictions of the two reduced-order models were found to be quite credible, too. Regarding the motion of the buoy, the obtained results indicate that, after being released from a height approximately equal to its draft at static equilibrium (which is about 60% of its radius), the buoy underwent nearly harmonic damped oscillations. The conducted analysis reveals that the draft length of the buoy has a profound effect on the frequency and attenuation rate of the oscillations. For example, compared to a spherical buoy of the same size that is half submerged at equilibrium (i.e., the draft is equal to the radius), the tested buoy oscillated with a period that was roughly 20% shorter, and its amplitude of oscillations decayed almost twice faster per period. Overall, the presented study provides additional insights into the motion response of a floating sphere that can be used for optimal buoy design for energy extraction

A Soft Optimization Model to Solve Space Allocation Problems in Breakbulk Terminals

In recent decades, freight transportation systems have been developed rapidly. This development leads to using various policies to enhance system utilization. The studies show that an optimized policy related to space allocation benefits the shareholders in freight transportations. The objective of space allocation problems is to find the best arrangement of cargos in warehouse cells to meet the problem aims. In this paper, inspired by the Office Space Allocation problem, we developed a novel model to minimize the handling costs and to maximize available spaces for the next arriving cargo. We first formulate the optimization model and discuss various constraints. We then present an approach to solve the proposed model. Lastly, we analyze a numerical example derived from the data of Port of Beaumont to illustrate the efficiency of the model

Predicting the price of second-hand vehicles using data mining techniques

The electronic commerce, known as “E-commerce”, has been boosted rapidly in recent years, and makes it possible to record all information such as price, location, customer’s review, search history, discount options, competitor’s price, and so on. Accessing to such rich source of data, companies can analyze their users’ behavior to improve the customer satisfaction as well as the revenue. This study aims to estimate the price of used light vehicles in a commercial website, Divar, which is a popular website in Iran for trading second-handed goods. At first, highlighted features were extracted from the description column using the three methods of Bag of Words (BOW), Latent Dirichlet Allocation (LDA), and Hierarchical Dirichlet Process (HDP). Second, a multiple linear regression model was fit to predict the product price based on its attributes and the highlighted features. The accuracy index of Actuals-Predictions Correlation, the min-max index, and MAPE methods were used to validate the proposed methods. Results showed that the BOW model is the best model with an Adjusted R-square of 0.7841

Fuzzy Modeling for Uncertain Nonlinear Systems Using Fuzzy Equations and Z-Numbers

In this paper, the uncertainty property is represented by Z-number as the coefficients and variables of the fuzzy equation. This modification for the fuzzy equation is suitable for nonlinear system modeling with uncertain parameters. Here, we use fuzzy equations as the models for the uncertain nonlinear systems. The modeling of the uncertain nonlinear systems is to find the coefficients of the fuzzy equation. However, it is very difficult to obtain Z-number coefficients of the fuzzy equations. Taking into consideration the modeling case at par with uncertain nonlinear systems, the implementation of neural network technique is contributed in the complex way of dealing the appropriate coefficients of the fuzzy equations. We use the neural network method to approximate Z-number coefficients of the fuzzy equations

Psychometric evaluation of Persian nomophobia questionnaire: differential item functioning and measurement invariance across gender

Background and aims: Research examining problematic mobile phone use has increased markedly over the past 5 years and has been related to “no mobile phone phobia” (so-called nomophobia). The 20-item Nomophobia Questionnaire (NMP-Q) is the only instrument that assesses nomophobia with an underlying theoretical structure and robust psychometric testing. This study aimed to confirm the construct validity of the Persian NMP-Q using Rasch and confirmatory factor analysis (CFA) models. Methods: After ensuring the linguistic validity, Rasch models were used to examine the unidimensionality of each Persian NMP-Q factor among 3,216 Iranian adolescents and CFAs were used to confirm its four-factor structure. Differential item functioning (DIF) and multigroup CFA were used to examine whether males and females interpreted the NMP-Q similarly, including item content and NMP-Q structure. Results: Each factor was unidimensional according to the Rach findings, and the four-factor structure was supported by CFA. Two items did not quite fit the Rasch models (Item 14: “I would be nervous because I could not know if someone had tried to get a hold of me;” Item 9: “If I could not check my smartphone for a while, I would feel a desire to check it”). No DIF items were found across gender and measurement invariance was supported in multigroup CFA across gender. Conclusions: Due to the satisfactory psychometric properties, it is concluded that the Persian NMP-Q can be used to assess nomophobia among adolescents. Moreover, NMP-Q users may compare its scores between genders in the knowledge that there are no score differences contributed by different understandings of NMP-Q items

Quantitative Assessment of Desertification Using Landsat Data on a Regional Scale – A Case Study in the Ordos Plateau, China

Desertification is a serious threat to the ecological environment and social economy in our world and there is a pressing need to develop a reasonable and reproducible method to assess it at different scales. In this paper, the Ordos Plateau in China was selected as the research region and a quantitative method for desertification assessment was developed by using Landsat MSS and TM/ETM+ data on a regional scale. In this method, NDVI, MSDI and land surface albedo were selected as assessment indicators of desertification to represent land surface conditions from vegetation biomass, landscape pattern and micrometeorology. Based on considering the effects of vegetation type and time of images acquired on assessment indictors, assessing rule sets were built and a decision tree approach was used to assess desertification of Ordos Plateau in 1980, 1990 and 2000. The average overall accuracy of three periods was higher than 90%. The results showed that although some local places of Ordos Plateau experienced an expanding trend of desertification, the trend of desertification of Ordos Plateau was an overall decrease in from 1980 to 2000. By analyzing the causes of desertification processes, it was found that climate change could benefit for the reversion of desertification from 1980 to 1990 at a regional scale and human activities might explain the expansion of desertification in this period; however human conservation activities were the main driving factor that induced the reversion of desertification from 1990 to 2000

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO