Simulation study of indirect positron generation by an ultra-short laser

Positron generation by an ultra-short ultra-intense laser in an indirect manner has been studied with two-dimensional particle-in-cell (PIC) and Monte Carlo (MC) simulations. In this generation scheme, positrons are produced with energetic electrons accelerated by an ultra-shot laser pulse propagating through an underdense plasma. The dependence of the positron beam properties on the plasma length and secondary target (converter) thickness was investigated in detail. The simulation results reveal that the positron yield is strongly correlated with the total energy of laser-accelerated electrons; both the temperature and divergence of the positron beam are sensitive to the plasma length; and the positron beam has a pulse duration comparable to the incident electron beam. In addition, it is indicated that even with the optimal converter thickness, only a small fraction (11.4%) of positrons can escape out and most of the detected positrons originate from the back edge of the converter

Optimization of positrons generation based on laser wakefield electron acceleration

Laser based positron represents a new particle source with short pulse duration and high charge density. Positron production based on laser wakefield electron acceleration (LWFA) has been investigated theoretically in this paper. Analytical expressions for positron spectra and yield have been obtained through a combination of LWFA and cascade shower theories. The maximum positron yield and corresponding converter thickness have been optimized as a function of driven laser power. Under the optimal condition, high energy (>100  MeV) positron yield up to 5×10^{11} can be produced by high power femtosecond lasers at ELI-NP. The percentage of positrons shows that a quasineutral electron-positron jet can be generated by setting the converter thickness greater than 5 radiation lengths

A comprehensive analysis of the Bencao (herbal) small RNA Atlas reveals novel RNA therapeutics for treating human diseases

Cross-kingdom herbal miRNA was first reported in 2012. Using a modified herbal extraction protocol, we obtained 73,677,287 sequences by RNA-seq from 245 traditional Chinese Medicine (TCM), of which 20,758,257 were unique sequences. We constructed a Bencao (herbal) small RNA (sRNA) Atlas ( http://bencao.bmicc.cn ), annotated the sequences by sequence-based clustering, and created a nomenclature system for Bencao sRNAs. The profiles of 21,757 miRNAs in the Atlas were highly consistent with those of plant miRNAs in miRBase. Using software tools, our results demonstrated that all human genes might be regulated by sRNAs from the Bencao sRNA Atlas, part of the predicted human target genes were experimentally validated, suggesting that Bencao sRNAs might be one of the main bioactive components of herbal medicines. We established roadmaps for oligonucleotide drugs development and optimization of TCM prescriptions. Moreover, the decoctosome, a lipo-nano particle consisting of 0.5%-2.5% of the decoction, demonstrated potent medical effects. We propose a Bencao (herbal) Index, including small-molecule compounds (SM), protein peptides (P), nucleic acid (N), non-nucleic and non-proteinogenic large-molecule compounds (LM) and elements from Mendeleev's periodic table (E), to quantitatively measure the medical effects of botanic medicine. The Bencao sRNA Atlas is a resource for developing gene-targeting oligonucleotide drugs and optimizing botanical medicine, and may provide potential remedies for the theory and practice of one medicine