The spin effect of electrons/positrons (e −/e +) and polarization effect of γ photons are investigated in the interaction of two counter-propagating linearly polarized laser pulses of peak intensity 8.9 × 1023 W cm−2 with a thin foil target. The processes of nonlinear Compton scattering and nonlinear Breit–Wheeler pair production based on the spin- and polarization-resolved probabilities are implemented into the particle-in-cell (PIC) algorithm by Monte Carlo methods. It is found from PIC simulations that the average degree of linear polarization of emitted γ photons can exceed 50%. This polarization effect leads to a reduced positron yield by about 10%. At some medium positron energies, the reduction can reach 20%. Furthermore, we also observe that the local spin polarization of e −/e + leads to a slight decrease of the positron yield about 2% and some anomalous phenomena about the positron spectrum and photon polarization at the high-energy range, due to spin-dependent photon emissions. Our results indicate that spin and polarization effects should be considered in calculating the pair production and laser-plasma interaction with the laser power of 10 PW to 100 PW classes.
When comets interacting with solar wind, straight and narrow plasma tails will be often formed. The most remarkable phenomenon of the plasma tails is the disconnection event, in which a plasma tail is uprooted from the comet’s head and moves away from the comet. In this paper, the interaction process between a comet and solar wind is simulated by using a laser-driven plasma cloud to hit a cylinder obstacle. A disconnected plasma tail is observed behind the obstacle by optical shadowgraphy and interferometry. Our particle-in-cell simulations show that the difference in thermal velocity between ions and electrons induces an electrostatic field behind the obstacle. This field can lead to the convergence of ions to the central region, resulting in a disconnected plasma tail. This electrostatic-field-induced model may be a possible explanation for the disconnection events of cometary tails.
Desalination of seawater has played an important role in many arid regions in the world. There are many methods for desalination of seawater, such as MED, MSF, RO, ED, TVC, and MVC, etc. Different methods have different advantages and disadvantages. In the present work, a new method for desalination of seawater with steam-ejector refrigeration plant was introduced. The main purpose of the new method is a hybrid plant of TVC and steam-ejector refrigeration. In the hybrid circle, no other energy was need. When the steam-ejector refrigeration plant is working, the seawater as cooling water is introduced into evaporator of TVC and evaporates. The vapor getting in TVC is extracted by a second steam-ejector, together with the active steam, is used as source of heat for desalination. The main advantage of this hybrid plant is that part of the heat energy of cooling water in refrigeration is reused. Comparing with other distillation method desalination of seawater, the energy consumption is much less. Especially on marine usage, the advantage is clear.
A folded dual-band monopole antenna for 2.45 GHz and 5.8 GHz RFID tag applications is proposed in the present paper. It is formed by two folded monopole antennas for reducing the geometric size of the tag. One of them operates at 2.45 GHz, and the other operates at 5.8 GHz. The input impedance of the proposed antenna is designed to be conjugate matched to the chip impedance for the maximum power transfer. This antenna is modeled, analyzed, and optimized by HFSS. The simulation results demonstrate that the performances of the proposed antenna can satisfy the requirements of RFID system. The characteristics of the proposed antenna are simple structure, low cost, and small sizes.
According to the structure feature of HTS magnet, heat transfer process in steady-state conditions is analyzed, and the heat conduction model of magnet unit was established. The thermal structure of conduction cooling HTS magnet was optimized to minimize the maximum temperature difference of magnet unit, and the optimization result was verified with simulation method. Simulation results show the optimization method mentioned in this paper is effective, which can provide a guidance to heat transfer structure design.
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