Net Charge Fluctuation and String Fragmentation

We present the simulation results of the net charge fluctuation in Au Au collisions at √Snn=130 GeV from a dynamic model, JPCIAE, and its revisions. The simulations are done for the quark-gluon matter, the directly produced pions, the pion matter, and the hadron matter. The simulated net charge fluctuation of the quark-gluon matter is close to the thermal model prediction for the quark-gluon gas. However, the discrepancy exists comparing the simulated net charge fluctuation for directly produced pions and the pion matter with the thermal model prediction for pion gas and the resonance pion gas, respectively. The net charge fluctuation of hadron matter from default JPCIAE simulations is nearly 3.5 times larger than quark-gluon matter. A discussion is given for the net charge fluctuation as an evidence of QGP phase transition.     

High order harmonic generation from solid targets: Towards intense attosecond pulses

Experiments and computer simulations on high order harmonic generation (HOHG) from steep plasma gradients using intense femtosecond laser pulses are presented. The importance of the plasma scale length for the efficiency of HOHG is demonstrated. By changing the pump intensity and the target parameters the regime of HOHG can be switched from non-relativistic to relativistic. Simulations show that attosecond pulses should already be present in our experiments in both interaction regimes. Two-color driven harmonic generation is shown to provide a highly efficient way of attosecond pulse production.     

高能核碰撞中带电多重数快度与能量和中心度的关系

用强子–弦级联模型JPCIAE及相应的Monte Carlo事例产生器研究相对论性核–核碰撞中带电粒子多重数的赝快度密度对能量和中心度的依赖关系.无需另调任何模型参数的条件下,此模型可以同时较好地描述相对论性pp实验数据及PHOBOS和PHENIX实验组的Au+Au实验数据.本文指出:因〈N_part〉并非严格定义的物理量,致使实验上和理论上确定〈N_part〉有一定任意性,从而使得每参加者核子对的带电粒子赝快度密度随着〈N_part〉的增加可能逐渐增大,也可能逐渐减小,因此用它来区分粒子产生机制是欠妥的.     

Timescales in the response of materials to femtosecond laser excitation

The interaction of ultrashort laser pulses with materials involves a number of special features that are different from laser–matter interaction for longer pulse durations. For femtosecond laser excitation the fundamental physical processes such as energy deposition, melting, and ablation are separated in time. By choosing proper time windows, the various processes can be investigated separately. We present selected examples of theoretical studies of free electron excitation in metals, timescales of different melting processes, and peculiarities of near-threshold ablation. Depending on the timescales and intensity ranges, the discussed processes are combined in an overall picture of possible pathways of the material from excitation to ablation. PACS 61.80.-x; 64.70.-p     

Adhesive interface interactions between primary aliphatic amine surface conditioners and polyamic ester/polyimide resins

The interface reactions of 3-aminopropyltriethoxysilane treated surfaces, with a polyamic alkyl ester/polyimide resin formed from pyromellitic dianhydride and oxydianiline, were defined by Fourier Transform Infrared (FTIR) analysis on the surface layers of germanium internal reflection plates. Adhesion between these interfacial layers is the result of chemical bonding, which apparently proceeds through initial amide formation between the amino function of the silylated surface and the alkyl ester group present in the polyamic ester. Heating results in diamide formation by a second alkyl, surface-bound amine displacing the aromatic polymer amine. Heating the more stable dialkyldiamide to 300°C imidizes both the polymer and the interfacial region, producing a strong laminate composite. Polymer scission at the aromatic amide linkages occurs in this adhesion process, bonding surface-bound alkyl amines to one end of a shortened polymer chain.     

Generation of isothermal density perturbations in the inflationary universe

It is shown that not only adiabatic perturbations of the density but also isothermal density perturbations are generated in the inflationary universe. The magnitude of isothermal perturbations can be sufficiently large for the subsequent galaxy formation. The spectrum of isothermal perturbations can differ considerably from a flat one.     

Characteristics of a hybridly mode-locked cw dye laser

We present experimental and theoretical results on the characteristics and random variations of subpicosecond pulses generated by a synchronously pumped cw dye laser with saturable absorber. The analysis of the power spectra indicates rapid fluctuations of the pulse duration of 40–50%, energy fluctuations of 3%, and a jitter of the repetition time of 0.1% corresponding to an absolute jitter of 12 ps. The latter is caused mainly by the temporal jitter of the pump laser. A mismatch of the lengths of the dye and the pump-laser cavity can result in a nonstationary mode-locking regime with a periodic change of the pulse parameters. The interpretation of the experimental results are supported by computer simulations of the pulse evolution process.