快速关联规则挖掘算法

关联规则挖掘是数据挖掘及知识发现领域的重要研究内容之一,其核心任务是挖掘数据库中的频繁项集。Apriori及其改良算法是频繁项集挖掘的有效算法。在类Apriori的算法中,它们都采用哈希树来存储频繁项集的候补项集以便快速计算其支持度。该文在仔细分析这些算法所存在的效率瓶颈的基础上,提出了另一个有效的改进算法。所提算法通过利用一个一维数组替代已有算法中的复杂的哈希树来达到改善它们效率瓶颈的目的。通过多个实验评估,该文所提算法的挖掘效率很高,比Apriori及其改良算法要快2到5倍。     

Deciphering Structural Alterations Associated with Activity Reductions of Genetic Polymorphisms in Cytochrome P450 2A6 Using Molecular Dynamics Simulations

Cytochrome P450 (CYP) 2A6 is a monooxygenase involved in the metabolism of various endogenous and exogenous chemicals, such as nicotine and therapeutic drugs. The genetic polymorphisms in CYP2A6 are a cause of individual variation in smoking behavior and drug toxicities. The enzymatic activities of the allelic variants of CYP2A6 were analyzed in previous studies. However, the three-dimensional structures of the mutants were not investigated, and the mechanisms underlying activity reduction remain unknown. In this study, to investigate the structural changes involved in the reduction in enzymatic activities, we performed molecular dynamics simulations for ten allelic mutants of CYP2A6. For the calculated wild type structure, no significant structural changes were observed in comparison with the experimental structure. On the other hand, the mutations affected the interaction with heme, substrates, and the redox partner. In CYP2A6.44, a structural change in the substrate access channel was also observed. Those structural effects could explain the alteration of enzymatic activity caused by the mutations. The results of simulations provide useful information regarding the relationship between genotype and phenotype.     

Virtual Alanine Scan of the Main Protease Active Site in Severe Acute Respiratory Syndrome Coronavirus 2

Recently, inhibitors of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro) have been proposed as potential therapeutic agents for COVID-19. Studying effects of amino acid mutations in the conformation of drug targets is necessary for anticipating drug resistance. In this study, with the structure of the SARS-CoV-2 Mpro complexed with a non-covalent inhibitor, we performed molecular dynamics (MD) simulations to determine the conformation of the complex when single amino acid residue in the active site is mutated. As a model of amino acid mutation, we constructed mutant proteins with one residue in the active site mutated to alanine. This method is called virtual alanine scan. The results of the MD simulations showed that the conformation and configuration of the ligand was changed for mutants H163A and E166A, although the structure of the whole protein and of the catalytic dyad did not change significantly, suggesting that mutations in His163 and Glu166 may be linked to drug resistance.     

Oxidation of carbon black over various Pt/MOx/SiC catalysts

Catalytic activities of various Pt/MO_x/SiC systems for carbon oxidation under simulated diesel exhaust gas were investigated in temperature-programmed reactions. When Pt/MO_x (MO_x=TiO₂, ZrO₂, Al₂O₃) was loaded onto silicon carbide (SiC), the oxidation activities became higher than those of Pt/MO_x alone or other Pt/MO_x/SiC systems (MO_x=Ta₂O₅, WO₃, Nb₂O₅, SnO₂, SiO₂, CeO₂, MoO₃, V₂O₅). Among them, Pt/TiO₂/SiC exhibited the highest activity. We discuss the activity of MO_x=TiO₂, ZrO₂, and Al₂O₃ in connection with NO oxidation activity, adsorption of sulfate onto the support, Pt dispersion, and specific surface area of the catalyst. Furthermore, we investigated the catalytic performance of Pt/TiO₂/SiC in more detail under isothermal conditions and in a staged arrangement.     

Pervaporation of methanol/dimethyl carbonate using SiO2 membranes with nano‐tuned pore sizes and surface chemistry

Porous silica membranes with different pore sizes (average pore size: 0.3–1.2 nm) and surface chemistry were prepared from SiO₂, steam‐treated SiO₂, SiO₂? ZrO₂, and SiO₂? TiO₂ by sol‐gel processing, and were applied to the pervaporation (PV) separation of methanol (MeOH) /dimethyl carbonate (DMC) mixtures at 50°C. Although SiO₂? ZrO₂ membranes demonstrated a separation factor of <10, the SiO₂ porous membranes had an increased separation factor from 10–160. Silica membranes with an average pore size of 0.3 nm showed the highest permselectivity of methanol with a separation factor of 140 and a methanol flux of 180 mol/(m²h) for MeOH 50 mol% at 50°C. To characterize the surface property of SiO₂ membranes, SiO₂ powdered samples were used for an adsorption experiment of vapor (MeOH, DMC) in single and mixed systems, revealing increased MeOH selective adsorption for SiO₂ powders with hydrophilic and small pores, which was consistent with PV performance. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Hydrogen fermentation properties of undiluted cow dung

Anaerobic treatment of undiluted cow dung (15% total solids), so-called dry fermentation, produced hydrogen (743 ml-H(2)/kg-cow dung) at an optimum temperature of 60 degrees C, with butyrate and acetate formation. The hydrogen production was inhibited by the addition of NH(4)(+) in a dose-dependent manner. A bacterium with similarity to Clostridium cellulosi was detected in the fermented dung by a 16S rDNA analysis.     

Removal of dilute benzene using a zeolite-hybrid plasma reactor

The decomposition of benzene was carried out using a plasma reactor packed with a mixture of BaTiO₃ and zeolite pellets, the zeolite-hybrid reactor. The reactor performance was characterized by measuring CO_x formed during plasma discharge and CO_x adsorbed on the solid surface, The decomposition efficiency of benzene in the hybrid reactor was 1.4-2.1× higher than that in a conventional plasma reactor packed with BaTiO₃ alone. Benzene existing outside a zeolite crystalline pore was found to decompose more easily than that inside a zeolite pore. In addition, the presence of zeolites suppressed the formation of NO_x     

Thermal design of a closed cabinet with a heat exchanger for inner air cooling

This paper describes a thermal design and simulation method of a closed cabinet with a heat exchanger for inner air cooling. In the controller system that we used for this research, the cabinet is equipped to be outdoors, and the cabinet is sealed to prevent the introduction of dust. Because this system dissipated 630 W in total, it suffered from a problem that the inner air temperature of the cabinet was raised over 30 K. Thus, we installed a heat pipe and heat exchanger in the cabinet, and we also changed the air flow path to realize the best performance of heat exchange according to the results from thermal and fluid simulations using a macroscopic model of heat exchanger to reduce the computational load. We found that the inner air temperature rise was reduced below 15 K, and the measured results were in good agreement with the simulation. © 2001 Scripta Technica, Heat Trans Asian Res, 30(4): 267–279, 2001     

Phylogenetic classification of Pseudomonas putida strains by MALDI-MS using ribosomal subunit proteins as biomarkers

A new method for phylogenetic classification of bacterial strains using matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is proposed. This method was developed using a bioinformatics-based approach to the rapid identification of bacteria as previously proposed by Demirev and co-workers, which uses ribosomal proteins composed of approximately 50 subunit proteins as biomarkers. Although the amino acid sequences of ribosomal proteins are highly conserved, slight sequence variations can occur at the strain level. Since ribosomal subunit proteins are a complex of housekeeping proteins that have different phylogenetic evolution rates, sequence variation detected as mass differences by MALDI-MS may be useful for the phylogenetic classification of bacteria at strain level. In our proposed method, the first step is the selection of reliable biomarkers through characterization of the expressed ribosomal subunit proteins of a reference strain (usually a genome-sequenced strain) by MALDI-MS. The observed masses in the MALDI mass spectra of cell lysates of sample strains are then compared with the biomarker masses of the reference strain. The biomarkers for each sample strain were designated as present or absent at the reference masses, indicated by 1 or 0, respectively, which were summarized in a table. This table is processed by cluster analysis, generating a phylogenetic tree. In this study, the success of this approach was confirmed by classification of Pseudomonas putida strains because its classification is much more complicated than that of other bacterial strains. Forty-three reliable biomarkers were selected from ribosomal sub-unit proteins of a genome-sequenced strain, P. putida KT2440. The numbers and kinds of biomarkers observed for 16 strains of P. putida, including different biovars, were markedly different, reflecting the variety of the strains. The classification results by the proposed method were highly comparable to those based on the DNA gyrase subunit B gene (gyrB) sequence analysis, suggesting our proposed method would be a useful high-throughput method for phylogenetic classification of newly isolated bacteria.