香蕉叶片Chla荧光动力学参量对激发光强的反应

在蓝色激发光(λ_m＝660nm)作用下,香蕉叶片的叶绿素a(Chla)发出波长为720～740nm的荧光信号,荧光强度随时间呈现有规律的变化.随着激发光强的增加,荧光动力学参量F₀和F_VI/F_V呈上升趋势,F_V/F₀与F_V/F_M逐渐达到饱和,而CA和T_1/2呈下降趋势.研究结果表明,保证香蕉叶片光合机构高速有序运转的适宜光强在20～60μmol·m^-2·s^-1之间,过量的光强将造成叶片光合机构的损伤.讨论了香蕉叶片诸荧光动力学参量的生物学意义及其随激发光强度增加而变化的原因.     

双折射光纤中偏振模色散的抑制

利用双折射光纤中孤子自捕获现象可以抑制偏振模色散,但这种抑制技术对传输参量有严格的限制.本文提出在双折射光纤中周期性地改变快慢轴的方法来抑制偏振模色散. 研究发现,这种方法在一定程度上能有效地抑制偏振模色散,并且光纤间偏振轴的夹角偏差有利于对偏振模色散的进一步抑制.     

Dihydrochalcones from Symplocos vacciniifolia

A new dihydrochalcone glucoside, vacciniifolin, along with confusoside, trilobatin and sieboldin were isolated from the leaves of Symplocos vacciniifolia. By the method of spectral analysis, this new compound was elucidated as 2‘,3,4,4‘-tetrahydroxydihydrochalcone 4‘-O-β-D-glu-copyranoside.     

Atemoyacin A: A new bis-tetrahydrofuranyl annonaceous acetogenin from Annona atemoya H.

Atemoyacin A, a new annonaceous acetogenin was isolated from the alcoholic extract of the seeds of Annona atemoya Hort (Annonaceae). Its structure and relative configuration were elucidated on the basis of the spectral analysis.     

AN ITERATIVE METHOD FOR THE MINIMAX PROBLEM

In this paper a class of iterative methods for the minimax problem i; proposed.We present a sequence of the extented linear-quadratic programming (ELQP) problems as subproblems of the original minimal problem and solve the ELQP problem iteratively.The locally linear and su-perlinear convergence results of the algorithm are established.     

THE WORST CASE COMPLEXITY OF THE FREDHOLM EQUATION OF THE SECOND KIND WITH FREE TERM IN H''''(Г)

This paper deals with the approximate solution of the Fredholm equation Lu= f of the second kind with f ∈H'(Γ). First, we give the order of the n-the optimal radius in the worst case setting. Then, we show that the Galerkin method using 2n+1 inner products of f has minimal error. Finally, we give the estimate of the ε-complexity of the Fredholm problem of the second kind and Galerkin method in the worst case setting.     

低电压扫描电子显微术

低电压扫描电子显微术是研究半导体、绝缘体和生物材料的有效方法。本文综述了这种方法的优点、限制和关于扫描电镜的改进,并且提供了实际操作的某些要领。     

Applying Digital Image Processing to SEM-EDX and BSE Images to Determine and Quantify Porosity and Salts with Depth in Porous Media

 Digital image processing is applied to X-ray element maps and back-scattered electron (BSE) images obtained with scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), to quantify and identify salts and porosity with depth in porous media. Until now, only salt chemical composition with depth has been characterised and salt mineral composition inferred, so that no salt quantification was possible. The method we present can be used stand-alone or integrated with other techniques to fill certain gaps in our knowledge. It can be used to quantify texture and porosity of clay minerals, with implications in petroleum research. Also, salts may be identified and quantified with depth in porous media; this is important when selecting among salt extraction procedures in order to conserve cultural heritage. Finally, the method can help in interpreting salt weathering processes and links between stone decay forms at different scales, with consequences for geomorphology. To demonstrate the method, salt and pore percentages with depth are determined in two limestone types from monuments in the Aunis province, SW France: i) Crazannes sparite, showing alveolisation and black crust, and ii) La Pallice micrite, suffering from micro-delamination. In most of the micrites no salts are identified. Porosity data show that micro-fissures are confined between the surface and 9 mm depth in LPAM5, the only micrite with loading salts with depth (NaCl = 1.9% at the surface versus 1.4% at 18 mm; and Na₂SO₄ · H₂O and MgCl₂ ∼ 0.02% in the first 3 mm). In the sparites, those samples with no crust display an alveolisation zone with lower porosity and higher diversity and percentage of salts. In CRZM6, the stone crust-alveolisation front lies at a depth of 9 mm. In the crust, porosity is lower than in the alveolisation zone (12%). Salt concentration, by contrast, is higher in the crust (2.91% versus 0.14% in the alveolisation zone). Received September 1, 2000 Revision November 2, 2001     

Intramolecular stacking interaction in mixed-ligand complexes containing ATP4- and aromatic N-heterocyclic ligands

The stability constants of the binary ML2+ and ternary M(ATP)L2- complexes,where L=Iq (isoquinoline) or BIm (benzimidazole) and M=Zn2+ or Cd2+,have been determined by poten-tiometric pH titration in aqueous solution at I=0.1 mol/L (NaClO4),T=25℃.The stability of the ternary complexes characterized by corresponding to the equilibrium M(ATP)2-+ML2+=M(ATP)L2-+M2+ is higher than what would be expected on statistical grounds.The increase may be related to the stacking interaction between the aromatic ring of the ligands L and the purine moiety of ATP4- 1H NMR studies of Zn2+/ATP4-/L confirm the presence of stacking in the ternary complexes.It is concluded that the strength of the intramolecular stacking interaction is dependent on the structure of the aromatic ring of the ligand L and the formation of a metal ion bridge.Possible implications are discussed briefly.