Efficient generation of relativistic near-single-cycle mid-infrared pulses in plasmas

Ultrashort intense optical pulses in the mid-infrared (mid-IR) region are very important for broad applications ranging from super-resolution spectroscopy to attosecond X-ray pulse generation and particle acceleration. However, currently, it is still difficult to produce few-cycle mid-IR pulses of relativistic intensities using standard optical techniques. Here, we propose and numerically demonstrate a novel scheme to produce these mid-IR pulses based on laser-driven plasma optical modulation. In this scheme, a plasma wake is first excited by an intense drive laser pulse in an underdense plasma, and a signal laser pulse initially at the same wavelength (1 micron) as that of the drive laser is subsequently injected into the plasma wake. The signal pulse is converted to a relativistic multi-millijoule near-single-cycle mid-IR pulse with a central wavelength of ~5 microns via frequency-downshifting, where the energy conversion efficiency is as high as approximately 30% when the drive and signal laser pulses are both at a few tens of millijoules at the beginning. Our scheme can be realized with terawatt-class kHz laser systems, which may bring new opportunities in high-field physics and ultrafast science

Inhibition of stimulated Raman scattering due to the excitation of stimulated Brillouin scattering

The nonlinear coupling between stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) of intense laser in underdense plasma is studied theoretically and numerically. Based upon the fluid model, their coupling equations are derived, and a threshold condition of plasma density perturbations due to SBS for the inhibition of SRS is given. Particle-in-cell simulations show that this condition can be achieved easily by SBS in the so-called fluid regime with kLλD<0.15, where kL is the Langmuir wave number and λD is the Debye length [Kline et al., Phys. Plasmas 13, 055906 (2006)]. SBS can reduce the saturation level of SRS and the temperature of electrons in both homogeneous and inhomogeneous plasma. Numerical simulations also show that this reduced SRS saturation is retained even if the fluid regime condition mentioned above is violated at a later time due to plasma heating

Laser pulse compression towards collapse and beyond in plasma

The dynamics of three-dimensional (3D) compression of ultrashort intense laser pulses in plasma is investigated theoretically and numerically. Starting from the slowly-varying envelope model, we derive equations describing the spatiotemporal evolution of a short laser pulse towards the singularity, or collapse, based on the variational method. In particular, the laser and plasma conditions leading to spherical compression are obtained. 3D particle-in-cell simulations are carried out to verify these conditions, which also enable one to examine the physical processes both towards and beyond the pulse collapse. Simulations suggest that the laser pulse can be spherically compressed down to a minimum size of the order of the laser wavelength, the so called lambda-cubic regime. The compression process develops over twice as fast in simulation than is predicted by the envelope model, due to the simplified nature of the latter. The final result of this process is pulse collapse, which is accompanied with strong plasma density modulation and spectrum broadening. The collapse can occur multiple times during the laser pulse propagation, until a significant part of the pulse energy is dissipated to electron acceleration by the laser ponderomitve force. It is also shown that a strong external DC magnetic field applied along the laser propagation direction can enhance the rate of compression for circularly-polarised laser pulses, when compared to an unmagnetised plasma, allowing access to strong compression and focusing in the low-density and low-amplitude regime

Tet3 regulates synaptic transmission and homeostatic plasticity via DNA oxidation and repair.

Contrary to the long-held belief that DNA methylation of terminally differentiated cells is permanent and essentially immutable, post-mitotic neurons exhibit extensive DNA demethylation. The cellular function of active DNA demethylation in neurons, however, remains largely unknown. Tet family proteins oxidize 5-methylcytosine to initiate active DNA demethylation through the base-excision repair (BER) pathway. We found that synaptic activity bi-directionally regulates neuronal Tet3 expression. Functionally, knockdown of Tet or inhibition of BER in hippocampal neurons elevated excitatory glutamatergic synaptic transmission, whereas overexpressing Tet3 or Tet1 catalytic domain decreased it. Furthermore, dysregulation of Tet3 signaling prevented homeostatic synaptic plasticity. Mechanistically, Tet3 dictated neuronal surface GluR1 levels. RNA-seq analyses further revealed a pivotal role of Tet3 in regulating gene expression in response to global synaptic activity changes. Thus, Tet3 serves as a synaptic activity sensor to epigenetically regulate fundamental properties and meta-plasticity of neurons via active DNA demethylation

Reanalyze unassigned reads in Sanger based metagenomic data using conserved gene adjacency

<p>Abstract</p> <p>Background</p> <p>Investigation of metagenomes provides greater insight into uncultured microbial communities. The improvement in sequencing technology, which yields a large amount of sequence data, has led to major breakthroughs in the field. However, at present, taxonomic binning tools for metagenomes discard 30-40% of Sanger sequencing data due to the stringency of BLAST cut-offs. In an attempt to provide a comprehensive overview of metagenomic data, we re-analyzed the discarded metagenomes by using less stringent cut-offs. Additionally, we introduced a new criterion, namely, the evolutionary conservation of adjacency between neighboring genes. To evaluate the feasibility of our approach, we re-analyzed discarded contigs and singletons from several environments with different levels of complexity. We also compared the consistency between our taxonomic binning and those reported in the original studies.</p> <p>Results</p> <p>Among the discarded data, we found that 23.7 ± 3.9% of singletons and 14.1 ± 1.0% of contigs were assigned to taxa. The recovery rates for singletons were higher than those for contigs. The <it>Pearson </it>correlation coefficient revealed a high degree of similarity (0.94 ± 0.03 at the phylum rank and 0.80 ± 0.11 at the family rank) between the proposed taxonomic binning approach and those reported in original studies. In addition, an evaluation using simulated data demonstrated the reliability of the proposed approach.</p> <p>Conclusions</p> <p>Our findings suggest that taking account of conserved neighboring gene adjacency improves taxonomic assignment when analyzing metagenomes using Sanger sequencing. In other words, utilizing the conserved gene order as a criterion will reduce the amount of data discarded when analyzing metagenomes.</p

Generation of GeV positron and γ-photon beams with controllable angular momentum by intense lasers

Although several laser–plasma-based methods have been proposed for generating energetic electrons, positrons and γ-photons, manipulation of their microstructures is still challenging, and their angular momentum control has not yet been achieved. Here, we present and numerically demonstrate an all-optical scheme to generate bright GeV γ-photon and positron beams with controllable angular momentum by use of two counter-propagating circularly-polarized lasers in a near-critical-density plasma. The plasma acts as a 'switching medium', where the trapped electrons first obtain angular momentum from the drive laser pulse and then transfer it to the γ-photons via nonlinear Compton scattering. Further through the multiphoton Breit–Wheeler process, dense energetic positron beams are efficiently generated, whose angular momentum can be well controlled by laser–plasma interactions. This opens up a promising and feasible way to produce ultra-bright GeV γ-photons and positron beams with desirable angular momentum for a wide range of scientific research and applications