Coherent Scattering of Light by Bose-Einstein Condensation in a Tight Confinement

We have observed strong scattering of a probe light by dilute Bose-Einstein condensate （BEC） ^87Rb gas in a tight magnetic trap. The scattering light forms fringes at the image plane. It is found that we can infer the real size of the condensation and the number of the atoms by modelling the imaging system. We present a quantitative calculation of light scattering by the condensed atoms. The calculation shows that the experimental results agree well with the prediction of the generalized diffraction theory, and thus we can directly observe the phase transition of BEC in a tight trap.     

Modified Woods-Saxon Potential for Heavy-Ion Fusion Reaction

A modified Woods-Saxon （MWS） potential is proposed for describing nucleus-nucleus interaction based on the Skyrme energy-density functional approach. Fusion barriers for a large number of fusion reactions from light to heavy systems can be described well with this potential. The suitable incident energies for fusion reactions leading to superheavy nuclei are also explored. It seems to us that the MWS potential is useful for selecting the suitable incident energies for fusion reactions for producing super-heavy nuclei.     

Ordered InAs Quantum Dots with Controllable Periods Grown on Stripe-Patterned GaAs Substrates

GaAs （001） substrates are patterned by electron beam lithography and wet chemical etching to control the nucleation of lnAs quantum dots （QDs）. InAs dots are grown on the stripe-patterned substrates by solid source molecular beam epitaxy. A thick buffer layer is deposited on the strip pattern before the deposition of InAs. To enhance the surface diffusion length of the In atoms, InAs is deposited with low growth rate and low As pressure. The AFM images show that distinct one-dimensionally ordered InAs QDs with homogeneous size distribution are created, and the QDs preferentiMly nucleate along the trench. With the increasing amount of deposited InAs and the spacing of the trenches, a number of QDs are formed beside the trenches. The distribution of additional QDs is long-range ordered, always along the trenchs rather than across the spacing regions.     

冬季冲绳海域地形及黑潮对声传播的影响

冲绳海域地形复杂且冬季存在较强的黑潮海洋锋,利用数值实验研究斜坡地形和海洋锋同时存在时由浅海至深海的声传播特性。海洋模式数值预报环境数据表明,分布于冲绳海槽斜坡上方的海洋锋导致该海域上层水体声速存在水平变化,纬度越高,水平变化越大。利用抛物方程声场模型计算声传播损失,通过简正模态分析存在表面声道的环境中声能量分布,利用声线轨迹图解释海底斜坡和海洋锋对声传播的影响。结果表明:声源频率低于表面声道截止频率时,声传播主要受海底地形影响;声源频率高于表面声道截止频率时,位于表面声道内的声源激发的声能量主要在表面声道传播,部分声能量从表面声道泄漏沿斜坡向深海传播,位于表面声道深度以下的声源激发的声能量主要沿斜坡向深海传播,斜坡地形导致表面声道下方至共轭深度这一深度范围呈现为声影区,海洋锋的存在可导致表面声道传播损失变化明显,影响程度与声源深度有关。     

HIRFL-CSRm内靶实验终端CsI(Tl)电磁量能器性能模拟

基于GEANT4模拟了HIRFL CSRm内靶实验终端的CsI(Tl)电磁量能器系统,给出了CsI电磁量能器的最佳设计参数及可能达到的性能.结果表明,设计的CsI(Tl)电磁量能器系统能够满足所研究的物理要求. Based on the GEANT4, the performance of the electromagnetic calorimeter (EMC) of the internal-target detector at HIRFL-CSRm is simulated. The simulation results show that 1.5%—3% of the energy resolution σ_E/E and 2° of the polar angular resolution σ_θ can be obtained. The invariant mass of the π~0 decay can be reconstructed well. The performance can meet the requirement of studying the proposed physics at HIRFL-CSRm.     

等离子体催化耦合重整生物质燃气研究

采用分步浸溃法制备了Ni-Mg整体式催化剂,加入萘作为焦油模型化合物考察了低温等离子体耦合催化重整生物质粗燃气的性能,研究了放电条件及反应温度对催化重整制备合成气的调变作用.结果表明:高压高频放电产生等离子体耦合催化重整,对重整净化生物质粗燃气有明显效果.在重整温度为750℃,放电频率为22 kHz时CH4的转化率可由催化重整时的86%提高到94%左右,放电条件下可以将合成气的H2/CO比由1.06提高至1.15.温度对耦合重整影响较为显著,CH4、CO2的转化率均随温度的升高而升高,最高可分别达到94%和89%.加入脉冲电晕后生物质粗燃气中的焦油等复杂有机化合物的转化率达到99%以上.     

Temperature－Induced Switching－Over of the Luminescence Transitions in GaInNAs／GaAs Quantum Wells

Photoluminescence (PL) spectra of the GaInNAs/GaAs single quantum well (SQW) with different N compositions are carefully studied in a range of temperatures and excitation power densities. The anomalous S-shape temperature dependence of the PL peak is analysed based on the competition and switching-over between the peaks related to N-induced localized states and the peak related to interband excitonic recombination. It is found that with increasing N composition, the localized energy increases and the turning point of the S-shape temperature dependence occurs at higher temperature, where the localized carriers in the handrail states obtain enough thermal activation energy to be dissociated and delocalized. The rapid thermal annealing (RTA)effectively reduces the localized energy and causes a decrease of the switching-over temperature.     

激光拉曼分光计中超低杂散光的测试

本文提出了一种测试激光拉曼分光计中超低杂散光的新方法.实验结果表明,本方法的杂散光测量限可达10~(-14)量级.     

用RHEED强度振荡锁相外延控制Ge/Si超晶格的生长

观察了Ge,Ge/Si交替外延时的反射式高能电子衍射(RHEED)强度振荡现象,并由此研究了Si(100)和Si(111)衬底上分子束外延Ge,Ge/Si超薄叠层的生长行为和生长特性。利用RHEED强度振荡,锁相控制生长了Ge(2ML)/Si(2ML),Ge(4ML)/Si(4ML)超薄超晶格。 关键词：