Bitcoin is a decentralized digital currency that has gained significant attention and growth in recent years. Unlike traditional currencies, Bitcoin does not rely on a centralized authority to control the supply, distribution, and verification of the validity of transactions. Instead, Bitcoin relies on a peer-to-peer (P2P) network of volunteers to distribute pending transactions and confirmed blocks, to verify transactions, and to collectively implement a replicated ledger that everyone agrees on. This P2P network is at the heart of Bitcoin and many other blockchain technologies. In this paper, we present a comparative measurement study of nodes in the Bitcoin network. We measure and analyze how many the so-called ''volunteers'' are in the Bitcoin P2P network by scanning the live Bitcoin network for 37 days in 2018 and compare them with the data reported by prior work in 2013∼2016. This paper is motivated by the fact that Bitcoin has experienced explosive growth in terms of a number of users, transactions, value, and interest over a recent couple of years. Our investigation includes the IP addresses of Bitcoin nodes, size of the network, power law in the geographic distribution, protocol, and client versions, and network latencies and shows how today's network is different from early days. In addition, based on the observations made from the measurement study, we propose a simple distance-based peer selection rule for improved connectivity and faster data propagation. The evaluation results show that our proposed lightweight and backward-compatible peer selection rule has the potential to reduce data dissemination latency. INDEX TERMS Bitcoin, peer-to-peer network, blockchain, peer selection, network measurement.

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Among the various biological routes for H production, dark fermentation is considered the most practically applicable owing to its capability to degrade organic wastes and high H production rate. Food waste (FW) has high carbohydrate content and easily hydrolysable in nature, exhibiting higher H production potential than that of other organic wastes. In this review article, first, the current status of H production from FW by dark fermentation and the strategies applied for enhanced performance are briefly summarized. Then, the technical and economic limitations of dark fermentation of FW are thoroughly discussed. Economic assessment revealed that the economic feasibility of H production from FW by dark fermentation is questionable. Current efforts to further increase H yield and waste removal efficiency are also introduced. Finally, future perspectives along with possible routes converting dark fermentation effluent to valuable fuels and chemicals are discussed.

Mutant strains of Escherichia coli have been isolated in which the synthesis of 3deoxy-D-arabinoheptulosonic acid 7-phosphate (DAHP) synthetase (phe) is derepressed, in addition to those enzymes of tyrosine biosynthesis previously shown to be controlled by the gene tyrR. The major enzyme of the terminal pathway of phenylalanine biosynthesis chorismate mutase-prephenate dehydratase is not derepressed in these strains. Genetic analysis of the mutants shows that the mutation or mutations causing derepression map close to previously reported tyrR mutations. A study of one of the mutations has shown it to be recessive to the wild-type allele in a diploid strain. It is proposed that the tyrR gene product is involved in the regulation of the synthesis of DAHP synthetase (phe) as well as the synthesis of DAHP synthetase (tyr), chorismate mutase-prephenate dehydrogenase, and transaminase A.The first reaction of aromatic biosynthesis, the condensation of erythrose-4-phosphate and phosphoenolpyruvate to form 3-deoxy-D-arabinoheptulosonic acid 7-phosphate (DAHP) is carried out in Escherichia coli by three isoenzymes, the synthesis and activity of each of these isoenzymes being controlled by tyrosine, phenylalanine, and tryptophan, respectively (4, 10, 17). These amino acids also control the synthesis of one or more enzymes in each of the terminal pathways from chorismic acid to tyrosine, phenylalanine, and tryptophan (10). In the case of tyrosine biosynthesis, the structural genes for DAHP synthetase (tyr) and chorismate mutaseprephenate dehydrogenase (a key enzyme in the tyrosine pathway) form a single operon, the expression of which is controlled by a regulator gene tyrR (Mattern and Pittard, in press). In tryptophan biosynthesis, the structural gene for DAHP synthetase (trp) is separated from the structural genes of the trp operon; however, all three are subject to control by the regulator gene trpR (5, 14; Camakaris and Pittard, in press).The genes for DAHP synthetase (phe) and chorismate mutase-prephenate dehydratase are also separated from each other on the chromosome; although operator mutants controlling the expression of the gene for chorismate mutase-prephenate dehydratase have been described (Im and Pittard, in press), there have as yet been no reports of mutations affecting the synthesis of DAHP synthetase (phe). It is the purpose of this paper to describe the isolation and characterization of mutants derepressed for the synthesis of DAHP synthetase (phe). Although the method that was used to isolate these mutants was expected to select for strains derepressed for both chorismate mutase-prephenate dehydratase and DAHP synthetase (phe), chorismate mutaseprephenate dehydratase is not derepressed in these mutants. However, the observation that the tyrosine biosynthetic enzymes are also derepressed in these mutants suggests the possibility of some relationship in the control of the two pathways.In an accompanying paper (4a), Brown and So-400 on July 15, 2020 by guest

This study investigated the impact of stimulating direct interspecies electron transfer (DIET), by supplementing nano-sized magnetite (nFe3O4, 0.5 g Fe/g VSS) and carbon nanotubes (CNT, 1 g/L), in anaerobic digestion of oleic acid (OA) at various concentrations (0.10–4.00 g chemical oxygen demand(COD)/L). Both supplementations could enhance CH4 production, and its beneficial impact increased with increased OA concentration. The biggest improvements of 114% and 165% compared to the control were achieved by nFe3O4 and CNT, respectively, at OA of 4 g COD/L. The enhancement can be attributed to the increased sludge conductivity: 7.1 ± 0.5 (control), 12.5 ± 0.8 (nFe3O4-added), and 15.7 ± 1.1 µS/cm (CNT-supplemented). Dissolved iron concentration, released from nFe3O4, seemed to have a negligible role in improving CH4 production. The excretion of electron shuttles, i.e., humic-like substances and protein-like substances, were found to be stimulated by supplementing nFe3O4 and CNT. Microbial diversity was found to be simplified under DIET-stimulating conditions, whereby five genera accounted for 88% of the total sequences in the control, while more than 82% were represented by only two genera (Methanotrix concilli and Methanosarcina flavescens) by supplementing nFe3O4 and CNT. In addition, the abudance of electro-active bacteria such as Syntrophomonas zehnderi was significantly increased from 17% to around 45%.