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61.
Alejandro J. Müller Maria Luisa Arnal Francisco López-Carrasquero 《Macromolecular Symposia》2002,183(1):199-204
We have recently prepared a series of Polystyrene-b-Poly(ethylene oxide)-b-Polycaprolactone (PS-b-PEO-b-PCL or SEOCL) triblock copolymers of varying compositions and molecular weights. These ABC triblock copolymers present the peculiarity that two of the three blocks are able to crystallize upon cooling from an already phase segregated melt. When either of the crystallizable blocks or both are a minor phase, a fractionated crystallization process develops. The confinement of crystallizable blocks in the nanoscopic scale enables the clear observation in some cases of exclusive crystallization from homogeneous nuclei of two components within the triblock copolymer. The homogeneous nature of the nucleation was deduced since the supercooling attained is the maximum possible before vitrification of the material takes place. The self-nucleation domains were also found to depend on the composition and molecular weight of the copolymers. The block copolymers exhibited a marked decrease in crystalline memory and when the crystallizable blocks constitute minor phases, the self-nucleation domain disappears. The reason behind this behavior is that only at lower self-nucleation temperatures the density of self-nuclei becomes high enough to include at least one crystal fragment per confined microdomain in view of their vast numbers (e.g., 1016/cm3). 相似文献
62.
Luisa Cervera M Carmen Arnal M de la Guardia M 《Analytical and bioanalytical chemistry》2003,375(6):820-825
The removal of heavy metals from wastewater by using activated alumina or chitosan as adsorbers was evaluated. Cd(II) and Cr(III) were employed as models of the behaviour of divalent and trivalent metal ions. The adsorption of Cd(II) and Cr(III) onto the adsorbers evaluated was studied as a function of pH, time, amount of adsorber, concentration of metal ions and sample volume. A 0.4-g portion of activated alumina can retain 0.6 mg Cr(III) and 0.2 mg Cd(II) from 20 mL sample adjusted at pH 4 and stirred for 30 min. It is therefore possible to totally decontaminate 500 mL of a waste containing 5 mg L(-1) Cd(II) and Cr(III) with 10 g alumina. On the other hand, 0.4 g chitosan can totally decontaminate 20 mL of a pH 5 solution containing up to 50 mg L(-1) Cd(II) and Cr(III). A 99.2+/-0.1% retention of Cd(II) and 83+/-1% retention of Cr(III) was obtained from 500 mL of a laboratory waste. The aforementioned strategies were applied for the minimization of analytical chemistry teaching laboratories and atomic spectrometry laboratory wastes. On comparing both adsorbers it can be concluded that chitosan is more preferable than alumina due to the reduced price of chitosan and the absence of side-pollution effects. 相似文献
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The laminar–turbulent transition of a forced oscillating boundary layer with a varying pressure gradient is experimentally and numerically investigated for two Strouhal numbers. Time-dependent characterization of the natural instability modes is carried out using continuous wavelet analysis of velocity signals. The periodic evolution of the total growth rates of the most unstable disturbances are measured and compared to the results of the linear stability theory. The “Tollmien–Schlichting” (TS) and “convective” transition modes are identified. It is shown that they correspond to the extrema of opposite signs of the skewness factor of unstable wavelet transform of the most unstable frequencies. 相似文献
66.
In the paper entitled “Separation of representations with quadratic overgroups”, we defined the notion of quadratic overgroups, and announced that the 6-dimensional nilpotent Lie algebra g6,20 admits such a quadratic overgroup. There is a mistake in the proof. The present Erratum explains that the proposed overgroup is only weakly quadratic, and g6,20 does not admit any natural quadratic overgroup. 相似文献
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68.
We prove that the irreducible representations with finite weight of discrete nilpotent groups of class 2, including the discrete Heisenberg groups, are monomial representations and obtain their classification for the group Heis(3, ?). 相似文献
69.
The measurement of low electron temperatures in a flowing unmagnetized argon plasma has been obtained by two methods: mutual impedance of a radiofrequency probe and of an electrostatic probe. The agreement between both methods is better than 5%. 相似文献
70.
Very large volume (>2 m3) homogeneous maxwellian plasmas in the 109?1010cm?3 density range have been easily obtained by using a microwave electron cyclotron resonance source operating at 2.45 GHz. The magnetic multiple device has proved its efficiency in confining plasmas containing no primary electrons. 相似文献