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

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Microbial fuel cell (MFC) research is a rapidly evolving field that lacks established terminology and methods for the analysis of system performance. This makes it difficult for researchers to compare devices on an equivalent basis. The construction and analysis of MFCs requires knowledge of different scientific and engineering fields, ranging from microbiology and electrochemistry to materials and environmental engineering. Describing MFC systems therefore involves an understanding of these different scientific and engineering principles. In this paper, we provide a review of the different materials and methods used to construct MFCs, techniques used to analyze system performance, and recommendations on what information to include in MFC studies and the most useful ways to present results.

Microbial Fuel Cells: Methodology and Technology†

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

Microbial fuel cells (MFCs) rely on electrochemically active bacteria to capture the chemical energy contained in organics and convert it to electrical energy. Bacteria develop biofilms on the MFC electrodes, allowing considerable conversion capacity and opportunities for extracellular electron transfer (EET). The present knowledge on EET is centred around two Gram-negative models, i.e. Shewanella and Geobacter species, as it is believed that Gram-positives cannot perform EET by themselves as the Gram-negatives can. To understand how bacteria form biofilms within MFCs and how their development, structure and viability affects electron transfer, we performed pure and co-culture experiments. Biofilm viability was maintained highest nearer the anode during closed circuit operation (current flowing), in contrast to when the anode was in open circuit (soluble electron acceptor) where viability was highest on top of the biofilm, furthest from the anode. Closed circuit anode Pseudomonas aeruginosa biofilms were considerably thinner compared to the open circuit anode (30 ± 3 μm and 42 ± 3 μm respectively), which is likely due to the higher energetic gain of soluble electron acceptors used. The two Gram-positive bacteria used only provided a fraction of current produced by the Gram-negative organisms. Power output of co-cultures Gram-positive Enterococcus faecium and either Gram-negative organisms, increased by 30-70% relative to the single cultures. Over time the co-culture biofilms segregated, in particular, Pseudomonas aeruginosa creating towers piercing through a thin, uniform layer of Enterococcus faecium. P. aeruginosa and E. faecium together generated a current of 1.8 ± 0.4 mA while alone they produced 0.9 ± 0.01 and 0.2 ± 0.05 mA respectively. We postulate that this segregation may be an essential difference in strategy for electron transfer and substrate capture between the Gram-negative and the Gram-positive bacteria used here.

/pdf/initial-development-and-structure-of-biofilms-on-microbial-1xzun8tgfu.pdf

Initial development and structure of biofilms on microbial fuel cell anodes

Microbial electrosynthesis from CO2: forever a promise?

Recently, bioelectrochemical systems (BESs) have emerged as a promising technology for energy and product recovery from wastewaters. To become economically viable, BESs need to (i) reach sufficient turnover rates at scale and (ii) generate a product that offsets the investment costs within a reasonable time frame. Here we used a liter scale, lamellar BES to produce a caustic solution at the cathode. The reactor was operated as a three-electrode system, in which the anode potential was fixed and power was supplied over the reactor to allow spontaneous anodic current generation. In laboratory conditions, with acetate as electron donor in the anode, the system generated up to 1.05 A (at 1.77 V applied cell voltage, 1015 A m−3 anode volume), and allowed for the production of caustic to 3.4 wt %, at an acetate to caustic efficiency of 61%. The reactor was subsequently operated on a brewery site, directly using effluent from the brewing process. Currents of up to 0.38 A were achieved within a six-week time fram...

High current generation coupled to caustic production using a lamellar bioelectrochemical system

Microbial fuel cell (MFC) anodes are anaerobic bioreactors. Processes such as fermentations and methanogenesis are likely competitors to electricity generation. This work studied the pathway of glucose conversion in continuous microbial fuel cell anodes with an adapted bacterial community. The study revealed that the majority of glucose is first fermented to hydrogen and acetate. Both are then used as substrates for bacterial electricity generation. When methanogens are present, methane production occurs at a rate that slightly increases with the current Methanogenesis and electricity generation compete for hydrogen, causing increased fermentation rates. In a rather young anodic biofilm on granular graphite, methanogenesis can be suppressed by aerating the anode compartment for one hour. Only short-term inhibition can be achieved applying the same technique on a well established biofilm on granular graphite. This study shows that fermentative processes are not detrimental to current generation, and that direct oxidation of glucose does not play a major role in mixed population conversions in a MFC anode.

Syntrophic processes drive the conversion of glucose in microbial fuel cell anodes

Nitrobenzene occurs as a pollutant in wastewaters originating from numerous industrial and agricultural activities. It needs to be removed prior to discharge to sewage treatment works because of its high toxicity and persistence. In this study, we investigated the use of a bioelectrochemical system (BES) to remove nitrobenzene at a cathode coupled to microbial oxidation of acetate at an anode. Effective removal of nitrobenzene at rates up to 1.29 +/- 0.04 mol m(-3) TCC d(-1) (total cathodic compartment, TCC) was achieved with concomitant energy recovery. Correspondingly, the formation rate for the reduction product aniline was 1.14 +/- 0.03 mol m(-3) TCC d(-1). Nitrobenzene removal and aniline formation rates were significantly enhanced when the BES was supplied with power, reaching 8.57 +/- 0.03 and 6.68 +/- 0.03 mol m(-3) TCC d(-1), respectively, at an energy consumption of 17.06 +/- 0.16 W m(-3) TCC (current density at 59.5 A m(-3) TCC). Compared to those of conventional anaerobic biological methods for nitrobenzene removal, the required dosage of organic cosubstrate was significantly reduced in this system. Although aniline was always identified as the major product of nitrobenzene reduction at the cathode of BES in this study, the Coulombic efficiencies of nitrobenzene removal and aniline formation were dependent on the current density of the BES.

Korneel Rabaey

Papers

Initial development and structure of biofilms on microbial fuel cell anodes

Microbial electrosynthesis from CO2: forever a promise?

High current generation coupled to caustic production using a lamellar bioelectrochemical system

Syntrophic processes drive the conversion of glucose in microbial fuel cell anodes

Nitrobenzene removal in bioelectrochemical systems.