Tetrapyrazinoporphyrazines with different number of peripheral pyridyl rings: Synthesis,photophysical and photochemical properties

Zinc tetrapyrazinoporphyrazines comprising different numbers of pyridin-2-yl and tert-butylsulfanyl substituents were prepared by the statistical condensation of two precursors – 5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile (A) and 5,6-dipyridin-2-yl-pyrazine-2,3-dicarbonitrile (B). The ensuing zinc tetrapyrazinoporphyrazines were chromatographically separated on silica column and characterized. Adjacent (AABB) and opposite (ABAB) isomers were not separated. The prepared zinc tetrapyrazinoporphyrazines did not differ in their Q-band position but the B-band position was shifted hypsochromically for compounds bearing more pyridyl units; in addition, a weak band at 450–520 nm decreased with increasing number of pyridyl substituents. Singlet oxygen quantum yields (Φ_Δ in the range 0.69–0.53) decreased with increasing number of pyridyl units on the macrocyclic core, while fluorescence quantum yields showed the reverse tendency (Φ_F in the range 0.22–0.26).     

Optical characterization of ultrananocrystalline diamond films

Optical properties of the ultrananocrystalline diamond films were studied by multi-sample method based on the combination of variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied in the range 0.6–6.5 eV. The films were deposited by PECVD in a conventional bell jar (ASTeX type) reactor using dual frequency discharge, microwave cavity plasma and radio frequency plasma inducing dc self-bias at a substrate holder. The optical model of the samples included a surface roughness described by the Rayleigh–Rice theory and a refractive index profile in which Drude approximation was used. The results conformed with the present understanding of the polycrystalline diamond growth on the silicon substrate because the existence of silicon carbide and amorphous hydrogenated carbon film between the silicon substrate and nucleation layer was proved.     

Synthesis of Gray Zirconium Silicate Pigments from Zircon Mineral

Zirconium silicate (zircon) pigments in new gray hues have been prepared from mineral zircon as a low-cost raw material. In the first step this material was deocmposed with a waste mixture of NaOH-KOH. In the second step the pigments were synthesized with addition of manganese, especially manganese(II) carbonate, as the chromophore. The optimum conditions for the syntheses of pigments have been estimated and the properties of products (hues, applicability to ceramic glazes) have been evaluated.     

Application of iterative dynamic programming to optimal control of a distiltation column

Iterative Dynamic Programming (IDP) is proven to be a useful technique for solving constrained dynamic optimisation problems. A high purity binary distillation column model has been chosen to investigate some of the IDP properties as well as its applicability. The investigated problems cover transitions from one steady state to another with the minimization of a quadratic cost function with associated terminal constraints.     

Preparation of hydrophobic poly(isobutylene) star polymers with hydrophilic poly(propylene imine) dendritic cores

Summary Poly(propylene imine) dendrimers with amino chain ends have been used for the preparation of hydrophobic star polymers with hydrophilic dendritic cores. The unsaturated end groups of polyisobutylene (PIB) were transformed into reactive anhydride end groups by an “ene” reaction with maleic anhydride, and the resulting functionalized PIB was then reacted with dendrimers to afford dendrimer-PIB star copolymers. Received: 20 May 1999/Accepted: 17 June 1999     

Synchrotron X-ray microdiffraction reveals rotational plastic deformation mechanisms in polycrystalline thin films

Understanding the mechanical response of polycrystalline materials on the mesoscopic scale remains a challenge as it is largely determined by grain-to-grain interactions and the discrete underlying microstructure. We conducted in situ synchrotron Laue microdiffraction experiments to map local strain tensors and orientations over polycrystalline thin gold films for different applied biaxial strain states. The experimental results demonstrate stress relaxation to be accompanied by cooperative transport of dislocation density leading to rotational plastic deformation heterogeneities. We propose a disclination model of closed dislocation walls and consider the geometry of transformations corresponding to a Burgers circuit enclosing the multipole disclination configuration. The observed stress-driven rotational deformation of the grain is shown to be described by the change in rotational closure failure associated with a Burgers circuit around the multipole disclination configuration. This concept is further advanced in a non-Euclidian geometry to demonstrate that the observed microrotation is captured by higher-order gradients in a micropolar continuum theory.     

捷克共和国的小水电工程

1捷克共和国发展水电潜能的自然条件 捷克共和国并没有建设水电站理想的自然条件。捷克的许多河流既没有所需的河川坡度，也没有充足的水量。因此，捷克共和国的水电在包括火电和核电的总发电量中的比例，是相当低的。最近由于2002年的洪水造成Vltava河的所谓Vltava梯级电站上的水电站的损坏，这一比例更加小了。     

SAR型模数转换器在电机控制电流测量中的应用

在电机控制系统中,设计者可通过周密分析获得理想的性能,即使开始看上去某些元件不合适.对于来自电流传感器的±5 V输出信号,则需要使用双电源(±12 V)的模数(A/D)转换器,TI公司推出的ADS7864型A/D转换器拥有同样效能,并给出了相关闭环电流互感器的应用.     

Averaging analysis of periodically forced fluid networks

For a lumped parameter model of a flow network driven by a periodic generator, we apply averaging to find an approximate solution and analyze its stability. The approximate solution has three parts: mean flow due to the resistive effects of branches, a time-periodic part due to “inductive” effects, and a mean flow average correction due to the interaction of nonlinear and time varying effects. We present an example that may explain the scenario leading to venous diseases. It is shown that the widening of a branch in a venous network leads to an increase in the AC flow and a decrease in the DC flow through that branch, thus increasing the stress on venous valves, and consequently leading to a further increase in the effective width of the vein.