ABSTRACT
WRKY‐type transcription factors are involved in multiple aspects of plant growth, development and stress response. WRKY genes have been found to be responsive to abiotic stresses; however, ...their roles in abiotic stress tolerance are largely unknown especially in crops. Here, we identified stress‐responsive WRKY genes from wheat (Triticum aestivum L.) and studied their functions in stress tolerance. Forty‐three putative TaWRKY genes were identified and two multiple stress‐induced genes, TaWRKY2 and TaWRKY19, were further characterized. TaWRKY2 and TaWRKY19 are nuclear proteins, and displayed specific binding to typical cis‐element W box. Transgenic Arabidopsis plants overexpressing TaWRKY2 exhibited salt and drought tolerance compared with controls. Overexpression of TaWRKY19 conferred tolerance to salt, drought and freezing stresses in transgenic plants. TaWRKY2 enhanced expressions of STZ and RD29B, and bound to their promoters. TaWRKY19 activated expressions of DREB2A, RD29A, RD29B and Cor6.6, and bound to DREB2A and Cor6.6 promoters. The two TaWRKY proteins may regulate the downstream genes through direct binding to the gene promoter or via indirect mechanism. Manipulation of TaWRKY2 and TaWRKY19 in wheat or other crops should improve their performance under various abiotic stress conditions.
WRKY‐type transcription factors are involved in multiple aspects of plant growth and development. Their roles in abiotic stress tolerance are largely unknown especially in crops. Here, we find that TaWRKY2 and TaWRKY19 from wheat play differential roles in abiotic stress tolerance through activation of different downstream genes.
A compact laser plasma accelerator (CLAPA) that can stably produce and transport proton ions with different energies less than 10 MeV,<1%energy spread, several to tens of pC charge, is demonstrated. ...The high current proton beam with continuous energy spectrum and a large divergence angle is generated by using a high contrast laser and micron thickness targets, which later is collected, analyzed and refocused by an image-relaying beam line using a combination of quadrupole and bending electromagnets. It eliminates the inherent defects of the laser-driven beams, realizes precise manipulation of the proton beams with reliability, availability, maintainability and inspectability (RAMI), and takes the first step towards applications of this new generation of accelerator. With the development of high-rep rate Petawatt (PW) laser technology, we can now envision a new generation of accelerator for many applications in the near future soon.
In order to implement radiotherapy based on a laser accelerator, it is necessary to precisely control the spatial distribution and energy spectrum of the proton beams to meet the requirements of the ...radiation dose distribution in the three-dimensional biological target. A compact laser plasma accelerator has been built at Peking University, which can reliably generate and transport MeV-energy protons with a specified energy onto the irradiation platform. In this paper, we discuss several technologies for the accurate control of a laser-accelerated proton beam with large divergence angle and broad energy spread, including the determination of the beam source position with micron accuracy, a tuning algorithm for the transport line which we refer to as “matching-image-point two-dimensional energy analysis” to realize accurate energy selection, and the control of beam distribution uniformity. In the prototype experiment with low energy protons and 0.5-Hz irradiation rate, a tailored energy deposition is demonstrated, which shows the potential feasibility of future irradiation based on laser-accelerated proton beams.
A deflection effect of an intense laser beam with spin angular momentum is revealed theoretically by an analytical modeling using radiation pressure and momentum balance of laser plasma interaction ...in the relativistic regime as a deviation from the law of reflection. The reflected beam deflects out of the plane of incidence with a deflection angle up to several milliradians, when a nonlinear polarized laser, with the intensity I_{0}∼10^{19}W/cm^{2} and duration around tens of femtoseconds, is obliquely incident and reflected by an overdense plasma target. This effect originates from the asymmetric radiation pressure caused by spin angular momentum of the laser photons. The dependence of the deflection angle of a Gaussian-type laser on the parameters of laser pulse and plasma foil is theoretically derived, which is also confirmed by three-dimensional particle-in-cell simulations of circularly polarized laser beams with the different intensity and pulse duration.
A novel approach for positron injection and acceleration in the laser driven plasma wakefield is proposed. One ring-shaped beam and one coaxially propagating Gaussian beam drive wakefields in a ...preformed plasma volume filled with both electrons and positrons. The laser’s ponderomotive force as well as the charge separation force in the front bucket of the first bubble are utilized to provide the transverse momenta of injected positrons and those positrons can be trapped by the focusing field and then accelerated by the wakefield. Theoretical analysis of the process is presented and verified by particle-in-cell simulations. The simulations show that relatively high-charge, quasimonoenergetic positron beams can be obtained.
The radiation reaction (RR) is expected to play a critical role in light-matter interactions at extreme intensity. Utilizing the theoretical analyses and three-dimensional (3D) numerical simulations, ...we demonstrate that electron reflection, induced by the RR in a head-on collision with an intense laser pulse, can provide pronounced signatures to discern the classical and quantum RR. In the classical regime, there is a precipitous threshold of laser intensity to achieve the whole electron bunch rebound. However, this threshold becomes a gradual transition in the quantum regime, where the electron bunch is quasi-isotropically scattered by the laser pulse and this process resembles a water splash. Leveraged on the derived dependence of classical radiation rebound on the parameters of laser pulses and electron bunches, a practical detecting method is proposed to distinguish the quantum discrete recoil and classical continuous RR force.
•Strain energy density method can be used to investigate the zonal disintegration.•The critical condition of zonal disintegration in deep rock mass is defined.•Stress-fields have wave feature when ...external load is more than critical value.•Rock mass displays elastic behavior when external load is less than critical value.
The deformation and failure modes of the deep rock mass are different from those of the shallow rock mass. Zonal disintegration phenomenon occurs in the deep rock mass, while loosened zone, plastic zone and elastic zone appear successively in the shallow rock mass. It is known that it is necessary to adopt the different support system for the different deformation and failure modes of rock mass. Therefore, it is very significant to define the critical condition of zonal disintegration. In this paper, a non-Euclidean model is proposed to investigate the critical condition of zonal disintegration in deep rock mass. A bulk free energy function of deep rock mass is introduced to describe the effects of microcracks. The standard formalism of non-equilibrium thermodynamics is used to obtain an equation for the non-Euclidean parameter. The relationship between non-Euclidean parameter and stress is established. The critical value of stress for zonal disintegration is derived using strain energy density approach. When the external load is less than the critical value of stress, the mechanical behaviors of rock materials can be simulated using the classical elastic model. In other words, when the external load is less than the critical value, zonal disintegration phenomenon does not occur. When the external load exceeds the critical value of stress, the mechanical behaviors of rock mass can be simulated using the non-Euclidean model, and zonal disintegration phenomenon occurs.
We report a proposal to observe the two-photon Breit-Wheeler process in plasma driven by compact lasers. A high-charge electron bunch can be generated from laser plasma wakefield acceleration when a ...tightly focused laser pulse propagates in a subcritical density plasma. The electron bunch scatters with the laser pulse coming from the opposite direction and resulting in the emission of high brilliance x-ray pulses. In a three-dimensional particle-in-cell simulation with a laser pulse of ∼10 J, one could produce an x-ray pulse with a photon number higher than 3×10^{11} and brilliance above 1.6×10^{23} photons/s/mm^{2}/mrad^{2}/0.1%BW at 1 MeV. The x-ray pulses collide in the plasma and create more than 1.1×10^{5} electron-positron pairs per shot. It is also found that the positrons can be accelerated transversely by a transverse electric field generated in the plasma, which enables the safe detection in the direction away from the laser pulses. This proposal enables the observation of the linear Breit-Wheeler process in a compact device with a single shot.
γ-ray flash generation in near-critical-density target irradiated by four symmetrical colliding laser pulses is numerically investigated. With peak intensities about 10^{23} W/cm^{2}, the laser ...pulses boost electron energy through direct laser acceleration, while pushing them inward with the ponderomotive force. After backscattering with counterpropagating laser, the accelerated electron is trapped in the electromagnetic standing waves or the ponderomotive potential well created by the coherent overlapping of the laser pulses, and emits γ-ray photons in a multiple-laser-scattering regime, where electrons act as a medium transferring energy from the laser to γ rays in the ponderomotive potential valley.
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