There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

비만아 부모의 돌봄 경험: q 방법론

Sequential anaerobic then aerobic composting was used to degrade polychlorinated biphenyls (PCBs). Changes in physical and chemical indicators in soil–compost mixture during the composting process were investigated. Differences in the PCB degradation rates under different conditions and different soil-to-organic waste ratios were assessed and the possible reasons for the differences were analyzed. The PCB concentrations decreased after 98 days of composting in each test treatment, but the PCB concentrations did not decrease significantly in the control (sterilized) experiments. This shows that the PCBs were dechlorinated and degraded because of microbial activity during the composting process. The results showed that aerobic composting coupled well with anaerobic composting. A two-stage composting and a relatively low soil-to-organic waste ratio (2:3) were advantageous for the degradation of PCBs, and the total PCBs degradation rate was 25.0 %. Composting with enriched and diversified microorganisms could offer advantages, when restoring contaminated sites, over other technologies that are available for biodegrading highly chlorinated PCBs.

Degradation of Polychlorinated Biphenyls by Sequential Anaerobic–Aerobic Composting

The bacterium Pseudomonas aeruginosa negatively regulates denitrification under anerobic conditions by two acyl-homoserine lactone quorum-sensing (QS) systems called las and rhl. However, it is unknown whether these systems have the same effect on denitrification in aerobic conditions. In this study, we investigated the regulation of las and rhl systems on aerobic denitrification. We showed that the removal of nitrate in P. aeruginosa PAO1 was repressed by both the las and rhl systems. The las and rhl systems had negative effects on activities of denitrifying enzymes NAP, NIR, NOR, and NOS. At the level of transcription, both QS systems inhibited the expression of target genes napA, nirS, norB, norC, and nosZ. Furthermore, the addition of an acylase, which degrades the acyl-homoserine lactone signals (AHLs), to wild type resulted in an increase in the removal of nitrate. Additionally, in aerobic denitrification process, the transcription factor DNR, which controls denitrification, was repressed by both QS systems. The results implied that modulation of QS in denitrifying bacteria, possibly through quorum quenching or QS inhibition, could help to improve the reduction of nitrate in wastewater treatment.

Regulation of las and rhl Quorum Sensing on Aerobic Denitrification in Pseudomonas aeruginosa PAO1

As the standard toxicity characteristic leaching procedure (TCLP) can not exhaust the acid neutralizing capacity of the cement rotary kiln co-processing solid wastes products which is particularly important for the assessment of the leaching concentrations of heavy metals. A modified TCLP was proposed. The extent of leaching of heavy metals is low using the TCLP and the leaching performance of the different metals can not be differentiated. Using the modified TCLP, however, Zn leaching was negligible during the first 180 h and then sharply increased (2.86 ± 0.18 to 3.54 ± 0.26 mg/L) as the acidity increased (pH < 6.0). Thus, Zn leaching is enhanced using the modified TCLP. While Pb leached readily during the first 126 h and then leachate concentrations decreased to below the analytical detection limit. To conclude, this modified TCLP is a more suitable method for these cement rotary kiln co-processing products.

Leaching Behavior of Heavy Metals from Cement Pastes Using a Modified Toxicity Characteristic Leaching Procedure (TCLP)

To develop a bacterial bioaugmentation system for fluorine-containing industrial wastewater treatment, optimal conditions for 4-fluoroaniline (4-FA) degradation and autoinducer release in Acinetobacter sp. TW were determined. Quorum sensing in biofilms of strain TW was also investigated. Different optimal conditions exist for 4-FA degradation and autoinducer release, particularly with regard to pH. Quorum sensing modulates extracellular polymeric substance (EPS) secretion and biofilm formation in the strain but plays no role in 4-FA degradation. Under optimal conditions for 4-FA degradation, the release of N-3-oxo-hexanoyl-homoserine lactone (3-oxo-C6-HSL) and N-hexanoyl-homoserine lactone (C6-HSL) in strain TW was significantly lower than required for quorum sensing. Under optimal conditions for autoinducer release, on the other hand, 3-oxo-C6-HSL and C6-HSL levels exceeded the quorum sensing thresholds, thereby inducing EPS secretion and biofilm formation. We conclude that the optimal conditions for autoinducer release (25 °C, pH 5, 800 mg L−1 4-FA, and 0 % NaCl) are suitable for bacterial colonization in bioaugmentation, while those for 4-FA degradation (25–30 °C, pH 8 and 800 mg L−1 4-FA) maximize the system performance after colonization.

Differences between 4-fluoroaniline degradation and autoinducer release by Acinetobacter sp. TW: implications for operating conditions in bacterial bioaugmentation

Pseudomonas aeruginosa uses quorum sensing (QS) to regulate the production of public goods such as the secreted protease elastase. P. aeruginosa requires the LasI-LasR QS circuit to induce elastase and enable growth on casein as the sole carbon and energy source. The LasI-LasR system also induces a second quorum-sensing circuit, the RhlI-RhlR system. During growth on casein, LasR-mutant social cheaters emerge, and this can lead to a population collapse. In a minimal medium containing ammonium sulfate as a nitrogen source populations do not collapse, cheaters and cooperators reach a stable equilibrium; however, without ammonium sulfate, cheaters overtake the cooperators and populations collapse. We show that ammonium sulfate enhances activity of the RhlI-RhlR system in casein medium and this leads to increased production of cyanide, which serves to control levels of cheaters. This enhancement of cyanide production occurs because of a trade-off in the metabolism of glycine: exogenous ammonium ion inhibits the transformation of glycine to 5,10-methylenetetrahydrofolate (5,10-methylene-THF) through a reduction in expression of the glycine cleavage genes gcvP1 and gcvP2, thereby increasing the availability of glycine as a substrate for RhlR-regulated hydrogen cyanide synthesis. Thus, environmental ammonia enhances cyanide production and stabilizes QS in populations of P. aeruginosa.

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Dongsheng Shen

Papers

Degradation of Polychlorinated Biphenyls by Sequential Anaerobic–Aerobic Composting

Regulation of las and rhl Quorum Sensing on Aerobic Denitrification in Pseudomonas aeruginosa PAO1

Leaching Behavior of Heavy Metals from Cement Pastes Using a Modified Toxicity Characteristic Leaching Procedure (TCLP)

Differences between 4-fluoroaniline degradation and autoinducer release by Acinetobacter sp. TW: implications for operating conditions in bacterial bioaugmentation

A Metabolic Trade-Off Modulates Policing of Social Cheaters in Populations of Pseudomonas aeruginosa.