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101.
Kurt Van Durme Bruno Van Mele Katrien V. Bernaerts Beatrice Verdonck Filip E. Du Prez 《Journal of Polymer Science.Polymer Physics》2006,44(2):461-469
A range of hydrophilic poly(methyl vinyl ether) (PMVE) polymers was synthesized by living cationic polymerization of methyl vinyl ether (MVE), having different hydrophilic or hydrophobic chain‐end functionalities. The dissimilar end‐groups were either introduced by end‐capping of the growing polymer chain with LiBH4, methanol, and water or by functional initiation with 2‐bromo‐(3,3‐diethoxy‐propyl)‐2‐methylpropanoate. The synthesized PMVEs were characterized by 1H NMR, size exclusion chromatography, and matrix‐assisted laser desorption ionization time of flight, displaying a narrow polydispersity. Modulated temperature DSC was applied to study the influence of the nature of the end‐groups on the solubility behavior of PMVE in water. Terminal‐modification with a hydroxyl function improves the solubility, whereas a Br‐containing end‐group causes the polymer to be insoluble in water at room temperature; however, the special type III lower critical solution temperature demixing behavior being maintained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 461–469, 2006 相似文献
102.
Magnetic energy losses have been investigated in Co-based near-zero-magnetostriction amorphous ribbons from DC to 10 MHz. Attention has been devoted to the properties of field-annealed ribbons thinned down to 5.8 μm and their behavior at high frequencies. A rationale is provided for the frequency dependence of the magnetic losses over the investigated many-decade range through analysis of the loss components. Ribbons annealed under transverse field benefit by limited irreversible domain wall activity and correspondingly reduced hysteresis and excess losses. Based on the near-linear response of the material and the permeability–energy loss relationship, the separate contributions of domain wall displacements and rotations to the magnetization process and the related dissipation effects are singled out at all frequencies. Very thin amorphous ribbons are shown to display lower loss and higher permeability (i.e. higher Snoek's product) than Mn–Zn ferrites at all frequencies. 相似文献
103.
Optimisation of poly-beta-hydroxyalkanoate analysis using gas chromatography for enhanced biological phosphorus removal systems 总被引:2,自引:0,他引:2
Oehmen A Keller-Lehmann B Zeng RJ Yuan Z Keller J 《Journal of chromatography. A》2005,1070(1-2):131-136
Poly-beta-hydroxyalkanoate (PHA) is a polymer commonly used in carbon and energy storage for many different bacterial cells. Polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), store PHA anaerobically through metabolism of carbon substrates such as acetate and propionate. Although poly-beta-hydroxybutyrate (PHB) and poly-beta-hydroxyvalerate (PHV) are commonly quantified using a previously developed gas chromatography (GC) method, poly-beta-hydroxy-2-methylvalerate (PH2MV) is seldom quantified despite the fact that it has been shown to be a key PHA fraction produced when PAOs or GAOs metabolise propionate. This paper presents two GC-based methods modified for extraction and quantification of PHB, PHV and PH2MV from enhanced biological phosphorus removal (EBPR) systems. For the extraction of PHB and PHV from acetate fed PAO and GAO cultures, a 3% sulfuric acid concentration and a 2-20 h digestion time is recommended, while a 10% sulfuric acid solution digested for 20h is recommended for PHV and PH2MV analysis from propionate fed EBPR systems. 相似文献
104.
Bonora M Becker J Saxena S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,170(2):617-283
We show the use of the observer blind spots effect for the elimination of electron spin-echo envelope modulation (ESEEM) peaks in double quantum coherence (DQC) electron spin resonance (ESR). The suppression of ESEEM facilitates the routine and unambiguous extraction of distances from DQC-ESR spectra. This is also the first demonstration of this challenging methodology on commercial instrumentation. 相似文献
105.
106.
We present an approach to quantum gauge theories formulated entirely on a superspace. We show that at the classical level the field equations are the same as in the usual Minkowski-space approach. In particular the a-flatness conditions, which represent the BRS and anti-BRS covariance in the usual approach, appear as field equations. We show that the theory is renormalizable and the a-flatness conditions are stable under renormalization. We speculate about the relevance of this approach to the confinement problem. 相似文献
107.
108.
Nutrition and health are closely connected and malnutrition can seriously endanger health. The consequences are higher risks of developing diseases. Of these, cancers are of special importance. The most frequent nutrition-associated type of cancer is colon cancer. This review summarises the predisposing factors for the development of colon cancer, and molecular mechanisms responsible for sporadic colon cancer. Moreover, it is pointed out that individual genetic predisposition such as polymorphisms of biotransformation systems might affect susceptibility to cancer risk factors. Selected findings of epidemiological research and nutritional habits, foods, and metabolites that could increase cancer risk are discussed. Furthermore, toxicological assessment of food-related risk factors, e.g. heterocyclic amines, and potential protective effects of food ingredients, e.g. the induction of phase II enzymes or removal of already degenerated cells from tissue by apoptosis, inhibition of proliferation, and cell differentiation are discussed. Risks are not necessarily reduced by avoiding certain substances but by healthy and well-balanced nutrition. Knowledge of individual susceptibility will also make it possible to recognise risks and design more specific nutritional recommendations. 相似文献
109.
Summary. By providing a matrix version of Koenig's theorem we reduce the problem of evaluating the coefficients of a monic factor
r(z) of degree h of a power series f(z) to that of approximating the first h entries in the first column of the inverse of an Toeplitz matrix in block Hessenberg form for sufficiently large values of n. This matrix is reduced to a band matrix if f(z) is a polynomial. We prove that the factorization problem can be also reduced to solving a matrix equation for an matrix X, where is a matrix power series whose coefficients are Toeplitz matrices. The function is reduced to a matrix polynomial of degree 2 if f(z) is a polynomial of degreeN and . These reductions allow us to devise a suitable algorithm, based on cyclic reduction and on the concept of displacement rank,
for generating a sequence of vectors that quadratically converges to the vector having as components the coefficients of the factor r(z). In the case of a polynomial f(z) of degree N, the cost of computing the entries of given is arithmetic operations, where is the cost of solving an Toeplitz-like system. In the case of analytic functions the cost depends on the numerical degree of the power series involved
in the computation. From the numerical experiments performed with several test polynomials and power series, the algorithm
has shown good numerical properties and promises to be a good candidate for implementing polynomial root-finders based on
recursive splitting strategies. Applications to solving spectral factorization problems and Markov chains are also shown.
Received September 9, 1998 / Revised version received November 14, 1999 / Published online February 5, 2001 相似文献
110.