Kähler-Einstein metrics with positive scalar curvature

In this paper, we prove that the existence of K?hler-Einstein metrics implies the stability of the underlying K?hler manifold in a suitable sense. In particular, this disproves a long-standing conjecture that a compact K?hler manifold admits K?hler-Einstein metrics if it has positive first Chern class and no nontrivial holomorphic vector fields. We will also establish an analytic criterion for the existence of K?hler-Einstein metrics. Our arguments also yield that the analytic criterion is satisfied on stable K?hler manifolds, provided that the partial C ⁰-estimate posed in [T6] is true. Oblatum 12-IV-1996 & 8-XI-1996     

激光调Q CAI

从激光调Q速率方程出发,分析推导了激光调Q过程中,腔内光子数与工作物质内反转粒子数间的关系.再根据激光调Q的过程中,对腔Q值控制方式不同,将激光调Q技术分为:转镜调Q、声光调Q、电光调Q、饱和吸收调Q和脉冲透射式调Q.用C语言进行了激光调Q CAI软件的开发研制,获得了将文学、图形、动画和计算融为一体的,直观而生动地将调Q的理论和过程再现于屏幕的CAI课件.介绍了课件的内容、结构及其特点.     

Preparation and structural stability investigation of CoN/CN soft X-ray multilayers

The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques. The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100–200 degrees centigrade through doping with N. The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400°C, and the interface pattern still exists even if they were annealed at 700°C. The Raman spectra analyses give the evidence that the formation of the sp³ bonding in the CN sublayers can be suppressed effectively by doping N with atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding betweenC andN atoms, and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc-Co and hcp-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420°C, leading to the suppression of the grain growth.     

全固态多波长飞秒脉冲激光系统

利用棱镜对引进频谱空间啁啾来补偿飞秒脉冲激光二次谐波产生中的相位失配,提高了倍频效率建立了一套全固态、多波长(1065nm, 532nm,823.1nm, 402nm)飞秒脉冲激光系统自制的Nd:YVO4激光器输出532nm绿光激光,最高平均功率可达5.6W当用2.5W绿光激光泵浦时,从自制的钛宝石激光器及经BBO倍频可分别输出中心波长为823.1nm和402nm,平均功率300mW和73mW,谱宽32.3nm和5.1nm,脉宽22fs和33.3fs、重复率108MHz的近红外和蓝光激光整个系统具有结构紧凑、倍频效率高、运行稳定的特点.     

Determination of ultra-trace gold in natural water by graphite furnace atomic absorption spectrophotometry after in situ enrichment with thiol cotton fiber

A simple method of determining ultra-trace Au in natural water was presented by using graphite furnace atomic absorption spectrophotometry (GFAAS) after in situ enrichment with thiol cotton fiber (TCF). The sample solution was adjusted to pH 1.5-2.0 with HCl, then the water sample was passed through a column packed with 0.10-0.20 g TCF and the flow rate was controlled at 20-40 ml min⁻¹. The effects of interferences, such as complexing and oxidizing agents and other elements adsorbed on TCF were overcome by chemical treatments prior to the desorption of Au. The adsorbed Au was adsorbed with 2.0 ml hot acid, then it was extracted with 1.00 ml methyl isobutylketone (MIBK). For a 5 l water sample, the detection limit of Au is 0.02 ng l⁻¹. The relative standard deviation (R.S.D.) for the determination of 1.44 ng l⁻¹ Au was 9.4%.The method was applied to determine ultra-trace Au both in suspended phase and soluble phase in natural water, the concentrations of total Au in natural water samples range from 0.51 to 67.82 ng l⁻¹. The recovery of added 0.50-6.00 ng l⁻¹ Au was 80-95%. The method is useful in prospecting for Au deposits by means of hydrogeochemical methods. The enrichment is carried out in the field, and then the determination of Au is completed later in the laboratory.     

厚高阶光学非线性介质Z扫描的变分法分析

利用变分法对具有五阶光学非线性介质的Z扫描特性进行了研究。通过比较，发现当介质在具有较大的五阶非线性系数或较大光强的情况下，五阶非线性项的作用是不可忽略的。这对光限制器的设计和Z扫描实验都具有一定的指导意义。     

Investigation on nonradiative decay of I13/2→I15/2 transition of Er-doped oxide glasses

Nonradiative decay of ⁴I_13/2→⁴I_15/2 transition of Er³⁺ has been investigated in a series of oxide glasses. For Er³⁺-doped glass samples, the Judd-Ofelt analysis on absorption spectra was performed and the fluorescence lifetime was determined by extrapolating to zero Er³⁺ concentration limit. Infrared spectra were measured in order to investigate the influence of OH⁻ groups in different glasses. The effects of glass matrix on the decay rate were discussed from the viewpoint of phonon energy, variations of effective fields, and OH⁻ groups. Compared to other glasses, phosphate glass presents low quantum efficiency and large nonradiative decay rate due to its high phonon energy and hygroscopic behavior.     

Comparative investigation of up-conversion luminescence in Tm/Yb-codoped germanate-niobic and germanium-bismuth glasses: effect of phonon density on up-conversion emission

Tm³⁺/Yb³⁺-codoped germanate-niobic (GN) and germanium-bismuth (GB) glasses have been synthesized by conventional melting and quenching method. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions ¹G₄→³H₆ and ¹G₄→³H₄, respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. GN glass showed a weaker up-conversion emission than GB glass, which is inconsistent with the prediction from the difference of maximum phonon energy between GN and GB glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Compared with phonon side-band spectroscopy, Raman spectroscopy extracts more information including both phonon energy and phonon density. For the first time, our results reveal that, besides the maximum phonon energy, the phonon density of host glasses is also an important factor in determining the up-conversion efficiency.