We report on overall enhancement of a single-stage laser wakefield acceleration (LWFA) using the ionization injection in a mixture of 0.3% nitrogen gas in 99.7% helium gas. Upon the interaction of 30-TW, 30-fs laser pulses with a gas jet of the above gas mixture, >300 MeV electron beams were generated at a helium plasma densities of 3.3-8.5 × 10(18) cm(-3). Compared with the uncontrolled electron self-injection in pure helium gas jet, the ionization injection process due to the presence of ultra-low nitrogen concentrations appears to be self-controlled; it has led to the generation of electron beams with higher energies, higher charge, lower density threshold for trapping, and a narrower energy spread without dark current (low energy electrons) or multiple bunches. It is foreseen that further optimization of such a scheme is expected to bring the electron beam energy-spread down to 1%, making them suitable for driving ultra-compact free-electron lasers.
2-Hydroxyphenazine (2-OH-PHZ) is an effective biocontrol
antibiotic
secreted by Pseudomonas chlororaphis GP72AN and is transformed from phenazine-1-carboxylic acid (PCA).
PCA is the main component of the recently registered biopesticide
“Shenqinmycin”. Previous research showed that 2-OH-PHZ
was better in controlling wheat take-all disease than PCA; however,
2-OH-PHZ production was low under natural conditions. Herein, we confirmed
that PCA induced reactive oxygen species in its host P. chlororaphis GP72AN and that the addition of DTT
improved PCA production by 1.8-fold, whereas the supplementation of
K3[Fe(CN)6] and H2O2 increased
the conversion rate of PCA to 2-OH-PHZ. Finally, a two-stage fermentation
strategy combining the addition of DTT at 12 h and H2O2 at 24 h enhanced 2-OH-PHZ production. Taken together, the
two-stage fermentation strategy was designed to enhance 2-OH-PHZ production
for the first time, and it provided a valuable reference for the fermentation
of other antibiotics.
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