A conformal invariant action for bosonic membranes is proposed by introducing intrinsic metric on world-tube. It is classically equivalent to the generalised Nambu-Goto action in the sense that the intrinsic metric be viewed at auxilliary field. Gauge fixing through BRST procedure is also carried out.

The infinite-dimensional algebras on two-dimensional torus are developed. In particular the diffeomorphism algebra and the Beltrami algebra on torus with their central extensions have been presented. It is shown that these algebras are corresponding to the diffeomorphism and the quasiconformal transformation of torus, respectively.

The N-N interaction is studied in the framework of non-relativistic quark model using the resonating group method (RGM). The ΔΔ channel is taken into account in addition to the NN channel. The calculated S-wave phase shifts show that the channel coupling effect is increased if the quadratic or the linear confinement is replaced by the Bat-bottom-linear confinement. This result is quite different from that in the case of the quadratic confinement or the linear confinement, in which this channel coupling effect is negligible.

We report the first experimental investigation of the photoionization cross-sec-tions of singlet excited ststes 3s5s¹S and 3s4d¹D in atomic magnesium, which can not be directly reached from the ground state. The measured absolute values are σ_3s5s¹S (571.lnm)=(0.27±0.09)Mb and σ_3s4d¹D (552. 8nm)=(2.6±0.9)Mb. Theoretical calculations were given, which are in good agreement with the measured values.

Autoionization spectra of atomic samarium have been observed using the stepwise laser excitation method. More than fifty autoionizating levels of Sm which are located in the 45793.9- 48045.4cm^-1 energy interval with odd parity have been measured.

High power tunable UV coherent radiation has been achieved by sum-frequency generation (SFG) in β-BaB₂O₄(BBO) crystal. The maximum output power obtained is about 3MW (near 368nm) and 0.75MW (near 222.5nm)

The H+-ions implantation and Ar⁺-ions bombardment did not cause near-surface decomposition of LiNbO₃, but it resulted in the alteration of the physical properties. The XPS (x-ray photoelectron energy spectroscopy) measurement was used to characterize the properties of the radiation damaged surface layer of LiNbO₃.

We report the results of the photoluminescence (PL) studies of the In_0.25Ga_0.75As-GaAs strained quantum wells (QW's) at 77K and at high pressures up to 50kbar. The pressure coefficients of the X valley of (InGa)As-GaAs strained QW's are presented for the first time. The crossover between the energy level in the well and the X valley in the barrier GaAs has been observed. The ratio of the conduction band offset to valence band offset in In_0.25Ga_0.75As-GaAs heterojunction was determined to be Q_c=ΔE_c :ΔE_v =0.68:0.32. Some discussions about GaAS – Al_0.3Ga_0.7 As QW's are also presented.

It has been found that the hydrogen-defect shallow donors do not appear, and some strong neutron radiation-induced Si-H IR bands, such as 1832 and 2054cm^-1 disappear; but the strength of some others, e.g. 1979 and 2065 cm^-1 increases greatly for NTD FZ(H₂) Si kept at room temperature for 3 years. These changes indicate that at room temperature simple point defects diffuse and interact, and hydrogen atoms trap the vacancy and vacancy cluster defects. This gives important information in the discussion of the micro-structures of the above Si-H IR bands.

The structural, magnetic and superconducting properties of the Tl₂Ba₂ (Ca_1-xMg_x)₂Cu₃O_y system with x=0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4,0.5 were studied. Replacement of calcium by magnesium depresses Tc from 116.3K (x=0) to 93.3K (x=0.5). The critical current also decreases with increasing x.

The ac magnetic susceptibility, the magnetoresistance R(H) and the dependence of the resistivity on temperature under different applied field were investigated in the Pb-doped Bi-Ca-Sr- Cu-O system. A superconducting phase with T_c~100K exists in this sintered sample. It forms a well connecting network, and therefore the Josephson coupling between the superconducting grains is sharply improved by doping lead.

The chemisorption of oxygen on Au (111) surface has been studied by low energy electron diffraction (LEED) and photoemission spectroscopy (PES). Oxygen was found to begin adsorbed on clean Au(ll1) surface at a temperature above 600°C and an oxygen pressure 5x10^-6mbar. The chemisorbed oxygen was very stable and could not be removed by heating up to 85°C . The widening of the Au 4f XPS peak and two new peaks in UPS were observed. The LEED observation showed that a structure with two twisted domains of hexagonal close packed oxide (AuO_x) overlayer was formed at the initial oxygen adsorption, and with further oxygen exposure another (√3 x√3 ) R30°structure was formed on the twisted oxide-overlayer.