A Cartesian grid-based boundary integral method for moving interface problems

This paper proposes a Cartesian grid-based boundary integral method for efficiently and stably solving two representative moving interface problems, the Hele-Shaw flow and the Stefan problem. Elliptic and parabolic partial differential equations (PDEs) are reformulated into boundary integral equations and are then solved with the matrix-free generalized minimal residual (GMRES) method. The evaluation of boundary integrals is performed by solving equivalent and simple interface problems with finite difference methods, allowing the use of fast PDE solvers, such as fast Fourier transform (FFT) and geometric multigrid methods. The interface curve is evolved utilizing the $\theta-L$ variables instead of the more commonly used $x-y$ variables. This choice simplifies the preservation of mesh quality during the interface evolution. In addition, the $\theta-L$ approach enables the design of efficient and stable time-stepping schemes to remove the stiffness that arises from the curvature term. Ample numerical examples, including simulations of complex viscous fingering and dendritic solidification problems, are presented to showcase the capability of the proposed method to handle challenging moving interface problems

Cloning and biochemical characterization of a novel lipolytic gene from activated sludge metagenome, and its gene product

In this study, a putative esterase, designated EstMY, was isolated from an activated sludge metagenomic library. The lipolytic gene was subcloned and expressed in Escherichia coli BL21 using the pET expression system. The gene estMY contained a 1,083 bp open reading frame (ORF) encoding a polypeptide of 360 amino acids with a molecular mass of 38 kDa. Sequence analysis indicated that it showed 71% and 52% amino acid identity to esterase/lipase from marine metagenome (ACL67845) and Burkholderia ubonensis Bu (ZP_02382719), respectively; and several conserved regions were identified, including the putative active site, GDSAG, a catalytic triad (Ser203, Asp301, and His327) and a HGGG conserved motif (starting from His133). The EstMY was determined to hydrolyse p-nitrophenyl (NP) esters of fatty acids with short chain lengths (≤C8). This EstMY exhibited the highest activity at 35°C and pH 8.5 respectively, by hydrolysis of p-NP caprylate. It also exhibited the same level of activity over wide temperature and pH spectra and in the presence of metal ions or detergents. The high level of stability of esterase EstMY with unique substrate specificities makes it highly valuable for downstream biotechnological applications

ADI schemes for heat equations with irregular boundaries and interfaces in 3D with applications

In this paper, efficient alternating direction implicit (ADI) schemes are proposed to solve three-dimensional heat equations with irregular boundaries and interfaces. Starting from the well-known Douglas-Gunn ADI scheme, a modified ADI scheme is constructed to mitigate the issue of accuracy loss in solving problems with time-dependent boundary conditions. The unconditional stability of the new ADI scheme is also rigorously proven with the Fourier analysis. Then, by combining the ADI schemes with a 1D kernel-free boundary integral (KFBI) method, KFBI-ADI schemes are developed to solve the heat equation with irregular boundaries. In 1D sub-problems of the KFBI-ADI schemes, the KFBI discretization takes advantage of the Cartesian grid and preserves the structure of the coefficient matrix so that the fast Thomas algorithm can be applied to solve the linear system efficiently. Second-order accuracy and unconditional stability of the KFBI-ADI schemes are verified through several numerical tests for both the heat equation and a reaction-diffusion equation. For the Stefan problem, which is a free boundary problem of the heat equation, a level set method is incorporated into the ADI method to capture the time-dependent interface. Numerical examples for simulating 3D dendritic solidification phenomenons are also presented

An On-line Test for Polycyclic Aromatic Hydrocarbons in the Flue Gas from Coal Combustion in an FBC System

Polycyclic Aromatic Hydrocarbons (PAHs) are environmental pollutants that have received considerable attention because of their carcinogenic and mutagenic effects. Due to the extensive amount of data suggesting the hazards of these compounds, 16 PAHs are on the Environmental Protection Agency (EPA) Priority Pollutant List. These compounds are often emitted into the atmosphere by way of combustion processes. Thus, analysis of these compounds during coal combustion is an important task. Three 1000-hour coal combustion burns were performed using the 0.1 MW (0.3 m) bench-scale Fluidized Bed Combustor (FBC) in the Combustion Laboratory at Western Kentucky University. The data for this thesis were collected from the second and third 1000-hour experiments. An in-situ sampling system was designed for 16 PAHs specified by EPA, which consisted of a glass wool filter, condenser, glass fiber filter, Teflon filter, and Tenax. The filters and Tenax were extracted by methylene chloride and hexane, respectively, followed by GC/MS analysis using the Selective Ion Monitoring (SIM) mode. The detection limits for each of the sixteen PAHs are as low as lppb. In this study, the effects of combustion temperature, combustion bed height, fluidizing velocity, excess air ratio, and the ratio of secondary air to primary air (air staging combustion) on the emissions of PAHs were studied. The results indicated that the emissions of PAHs in an FBC system were dependent on the combustion conditions. PAHs are mainly produced by incomplete combustion. Incomplete combustion results in larger PAHs with four or more benzene rings. High efficiency combustion results in smaller PAHs with two or three benzene rings

The influence of users' Dark Triad on knowledge contribution behaviour on social Q&A sites

The users' knowledge contribution behavior is the driving force for the sustainable development of the social Q&A sites. This kind of user behavior is affected by various factors, among which users' personality traits are the prominent ones. The dark triad is a theory on the dark side of personality. This article explores the influence and mechanism of users' dark triad on their knowledge contribution in social Q&A sites. A questionnaire survey was conducted on 301 users with experience in social Q&A sites. The survey data were then analyzed by hierarchical regression and Bootstrap analysis. The dark triad significantly affects knowledge contribution on social Q & A sites. Online self-disclosure plays a completely mediating role in the relationship between the dark triad and knowledge contribution. The relational psychological contract has a moderating role between online self-disclosure and knowledge contribution. This study argues that the dark triad has a positive effect on knowledge contribution behavior in socialized Q&A communities by constructing a model of mediated effects that are moderated. The dark triad shows its altruistic side in the context of social Q&A sites. The role of the dark triad in different knowledge-intensive contexts should be viewed dialectically in future research. Based on these findings, we put forward some suggestions for encouraging users' knowledge contribution behavior in the social media context.Peer Reviewe