Next generation petawatt laser facility is expected to reach intensity up to the order of 10²³-10²⁴ W·cm^-2,which may generate electromagnetic fields so strong that nonlinear quantum electrodynamics (QED) processes play a crucial role in plasma dynamics.A large number of γ photons can be emitted through synchrotron radiation from ultrarelativistic electrons,and pair creation process can also be triggered when γ photons traverse electromagnetic fields.In turn,these QED physics can affect plasma dynamics itself significantly,in particular for electron motion under radiation reaction.In order to study such extreme plasma dynamics,we introduce a QED model developed in recent years,which can be coupled with traditional particle-in-cell (PIC) code,i.e.,so-called a QED-PIC code.Due to booming particle number caused by the newly emitted photons and created pairs,we also develop a particle merge algorithm to reduce the computational scale.Several applications of this contemporary QED-PIC code in modeling of ultraintense laser-plasma interaction and extreme astrophysical phenomena are presented.

Physics and mathematics model for three-dimensional bladder filling estimation are constructed for electrical impedance tomography.Verification was carried out with combined Tikhonov regularization algorithm.Reconstruction results with high spatial resolution,high stability and enhanced anti-noise performance were obtained.With Laplacian analysis of calculation results,boundary was extracted and processed.As a result,integration boundary surface fragments were extracted from high noise background in morphological characteristics of the object.Ultimately,three-dimensional image reconstruction was achieved.Compared with two-dimensional imaging,it provided spatial position,height and spatial contrast for qualitative analysis.

A 4-layer sphere model of human head is built for the forward problem of magnetic induction tomography.The layers represent the brain,the CFS,the skull,and the scalp respectively.Taking vector magnetic potential as a variable,Helmholtz equation in a spherical coordinates is constructed as a control equation of the forward problem.A variables separation method is used to solve the equations with boundary and interface conditions.Distribution of the magnetic vector potential and eddy current in the model are obtained.Equi-potential lines of the eddy current are given.Influence of frequency and magnitude of the exciting current on the induced voltage is analyzed.The algorithm is validated by solving a forward problem of magnetic induction tomography.It can be used as a fast algorithm to generate sensitivity matrix in an inverse problem.

A 4-layer sphere model of human head is built.Layers from outside to inside represent scalp,skull,CFS and brain,respectively.The point current source placed on the outmost layer is regarded as boundary condition.A method of separation of variables is used to solve the equations.Potential distributions with different injecting angles are shown.We simulate conductivity distribution of brain tissue, and plot real and imaginary potentials at nine points on the outmost layer.As conductivity of brain tissue changes,the real potentials vary greatly than the imaginary parts.Frequency characteristic is simulated,and the result shows that the imaginary potentials on the outmost layer is influenced mostly by frequency.These can be used in analyzing head EIT problems and improving the Back-projection Algorithm.