Ultrasonic depolymerization of aqueous polyvinyl alcohol.

Ultrasonication has proved to be a highly advantageous method for depolymerizing macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature of the polymer. Most of the effects involved in controlling molecular weight can be attributed to the large shear gradients and shock waves generated around collapsing cavitation bubbles. In general, for any polymer degradation process to become acceptable to industry, it is necessary to be able to specify the sonication conditions which lead to a particular relative molar mass distribution. This necessitates the identification of the appropriate irradiation power, temperature, concentration and irradiation time. According to the results of this study the reactors constructed worked well in depolymerization and it was possible to degrade aqueous polyvinyl alcohol (PVA) polymer with ultrasound. The most extensive degradation took place at the lowest frequency used in this study, i.e. 23 kHz, when the input power was above the cavitation threshold and at the lowest test concentration of PVA, i.e. 1% (w/w). Thus this study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to therefore become smaller.     

Studies on adhesion characteristics and corrosion behaviour of vinyltriethoxysilane/epoxy coating protective system on aluminium

The corrosion stability of vinyltriethoxysilane/epoxy coating protective system on aluminium is strongly related to the strength of bonds forming at the metal/organic coating interface. This article is a study of adhesion, composition, electrochemical and transport properties of epoxy coatings electrodeposited on bare aluminium and aluminium pretreated by vinyltriethoxysilane (VTES) during exposure to 3% NaCl. The VTES film was deposited on aluminium surface from 2% vinyltriethoxysilane solution during 30 s. From the values of adhesion strength (pull-off test), time dependence of pore resistance and coating capacitance of epoxy coating (impedance measurements) and diffusion coefficient of water through epoxy coating (gravimetric liquid sorption measurements), the influence of VTES sublayer on the corrosion stability of the electrodeposited epoxy coating was shown.The work discusses the role of the VTES pretreatment in the enhanced adhesion and corrosion stability of epoxy cataphoretic coating. The electrochemical results showed that the aluminium pretreatment by VTES film improved barrier properties of epoxy coating (greater pore resistance and lower coating capacitance). The lower value of diffusion coefficient of water through epoxy coating indicates the lower porosity, while the smaller adhesion reduction points to better adhesion of epoxy coating on aluminium pretreated by VTES film. The composition of the deposited coatings investigated by XPS enabled the clarification of the bonding mechanism.     

Ion synthesis and optical properties of gold nanoparticles in an Al2O3 matrix

Single-crystal Al₂O₃(0001) and Al₂O₃(1120) substrates are implanted by 160-keV Au⁺ ions with doses from 10¹⁵ to 10¹⁷ cm^?2. Some of the implanted samples are air-annealed at 800–1200°C. The properties of the synthesized composite layers are studied by Rutherford backscattering and linear optical reflection measurements, and their nonlinear optical characteristics are examined by RZ-scanning using a picosecond Nd: YAG laser operating at a wavelength of 1064 nm. The Rutherford backscattering spectra indicate that the implanted impurity concentrates near the surface of the Al₂O₃. The formation of gold nanoparticles in the Al₂O₃ can be judged from the characteristic optical plasmon resonance band in the reflectance spectra of the samples irradiated to a dose higher than 6.0 × 10¹⁶ cm^?2. The synthesized particles are shown to be responsible for nonlinear optical refraction in the samples. The nonlinear refractive index, n ₂, and the real part of the third-order susceptibility, Rex⁽³⁾, of the composite layers are determined.     

通过有光阑近轴ABCD光学系统激光束的近似解析传输公式

用傅立叶级数展开法研究光束通过有光阑限制的近轴ABCD光学系统的传输特性,导出了光阑透射率函数不同时的传输公式。硬边光阑的情况可作为其它光阑的特例得到,其它光阑也可视作硬边光阑来处理。数值计算表明了该方法快速的优点,并得到与用Collins公式直接积分一致结果。     

激光对红外系统的失效机理和破坏效应研究

根据红外光学系统的会聚特性,用光学增益方法分析了红外系统中各元件对应的光强分布,确定了位于焦面附近光学元件是激光破坏的易损部件,并提出了强激光对红外系统元件损伤,造成其探测、制导功能失效的硬破坏机理;由红外滤光片、探测器和信号处理电路与入射激光波长的光谱响应分析,提出了弱激光对红外系统干扰,导致其探测、制导功能在激光辐照一段时间内失效的软破坏机理;开展了激光辐照红外系统的失效验证实验,较好地解释了其失效的机理和效应。     

Elimination of the type B uncertainty

An uncertainty of an estimated parameter can be, in general, decomposed into two parts, i.e. an uncertainty caused by errors in the actual experiment (the type A uncertainty) and an uncertainty caused by errors in preceding experiment, where some wanted constants were estimated (the type B uncertainty). These constants are necessary for an estimation of the useful parameters. The aim of the paper is to find a condition for elimination of the type B uncertainty.     

Concentration variations in the optical pseudogap and refractive index of crystals of Cu6PS5I1–xClx solid solutions

The effect of anionic substitution of halogen atoms on the spectral position and shape of the optical absorption edge and the dispersion of the refractive index of crystals of Cu₆PS₅I_1–xCl_x solid solutions are studied. The concentration dependences of the width of the optical pseudogap, refractive index, and lattice parameters are shown to be interrelated in these solid solution crystals.