Collision of counterpropagating laser-excited wake bubbles.

The collision of wake bubbles behind two counterpropagating laser pulses in rarefied plasma is investigated using particle-in-cell simulation. Special attention is paid to the highly nonlinear dynamics of the electrons in the interaction region. It is found that, as the two bubbles approach each other and collide, the electrons in the interaction region first oscillate in a periodic fashion, forming a quasistationary dense electron density ripple with fairly regular spatial structure. At longer times, the electron motion becomes chaotic, and the density grating is gradually smeared. The electrons escape in the transverse direction, and eventually the two bubbles merge to form a single one. The transition of the electron motion from regular to chaotic is confirmed by analytical modeling using test electrons moving in counterpropagating planar electromagnetic waves. The findings shed light on the dynamics of wake-bubble collisions and the complex behavior induced by multiple laser pulses in plasmas.

Corrections to scaling for the two-dimensional dynamic XY model.

With large-scale Monte Carlo simulations, we confirm that for the two-dimensional XY model, there is a logarithmic correction to scaling in the dynamic relaxation starting from a completely disordered state, while only an inverse power law correction in the case of starting from an ordered state. The dynamic exponent z is z=2.04(1).

[Studies on the chemical constituents of Carduus crispus L].

OBJECTIVE: To study the chemical constituents of Carduus crispus. METHOD: Using chromatographic methods to isolate compounds and using chemical and spectral methods to elucidate the structures of the isolated compounds. RESULT: Eight compounds were elucidated as beta-amyrin palmitate, taraxastery acetate, luteolin-7-O-alpha-L-rhamanopyranosyl-(1-->2)-beta-D-glucopyranoside, luteolin-7-O-beta-D-glucopyranoside, triacontanic acid, beta-sitosterol, stigmasterol and stigmast-7-en-3 beta-ol. CONCLUSION: All the compounds were obtained from this plant for the first time.