Zur Kenntnis des m,m′-Divinylazobenzols und des m,m′-Divinylazoxybenzols

Ohne Zusammenfassung     

Das anodische Verhalten von Acetationen in nichtwäßriger Lösung an einer rotierenden Platinscheibenelektrode

Acetate ions are irreversibly oxidized in nonaqueous solutions. The electron transfer reaction is believed to be the rate determining step. Increasing addition of acetic acid which itself is not oxidized shifts the half wave potential towards more positive values. This change is interpreted in terms of the formation of a 1:1 complex between acetate ions and acetic acid. This shift allows to obtain a polarographic wave forDMF in acetic acid-acetate system although the acetate ions on their part give a polarographic wave inDMF.     

Über den Mechanismus der Wachstumsreaktion mikroorientierter Polymerer (Popcornwachstum)

Zusammenfassung Die Zerteilungsphänomene beim Wachstum eines mikroorientierten Styrol-p-Divinylbenzolcopolymeren (Popcornpolymeren) in monomerem Styrol werden beschrieben.Für den Fall des Wachstums eines 2,5-Dichlorstyrol-p-Divinylbenzolcopolymeren in monomerem Styrol wird die Zerteilung durch Bestimmung des Chlorgehalts in den verschiedenen Teilen des Endpolymerisats quantitativ bestimmt. Angaben über Quellungsgrad und Hohlraumgehalt der Popcornpolymeren werden gemacht. Der Gehalt an anhängenden Doppelbindungen, die Wachstumsgeschwindigkeit sowie der Start des Wachstums werden diskutiert.

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Splitting up effects during the growth of a microoriented styrene p-divinylbenzene copolymer (popcorn polymer) in styrene monomer are described. For the growth of a 2,5-dichlorostyrene-p-divinylbenzene copolymer in styrene monomer the splitting up is quantitatively followed by determining the chlorine content in the different parts of the end polymer. Data on swelling and void content of the popcorn polymers are presented. A discussion of the number of pendant double bonds, growth rate and initiation of growth is given.

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Mit 7 Abbildungen     

Parity violation in pion-proton scattering

Parity-violating pion-proton scattering is strongly dominated by so-called penguin operators. These operators are due to the presence of the neutral current, and their strength is further enhanced by the QCD renormalization effects. Without such contributions the elastic asymmetry (A_l) would be an order of magnitude smaller (up to 150 MeV of the pion laboratory kinetic energy). Possible contributions from the resonance poles (?-meson, ($\text{1}\text{2}{}^{\mathrm{+}}\text{)}{}^1\text{-}\text{reson}$) have been also included. Thus pion scattering on the polarized proton can test the commonly-used effective QCD renormalized weak hamiltonian.     

Studies of silicophosphate derivatives by 31P-->29Si CP MAS NMR

We show that it is possible to efficiently transfer magnetization from ³¹P to ²⁹Si, using variable amplitude CP MAS experiment. This experiment is demonstrated by using Si₅O(PO₄)₆, the synthesis protocol of which is described. From the obtained results, we show that the experiment allows the spectral edition of ²⁹Si spectra from ³¹P→²⁹Si CP, enabling the studies of derivatives involving Si–O–P linkages, such as phosphosilicate glasses, microporous silicoaluminophosphates (SAPO) and bioactive phosphosilicates.     

Monotonicity inequalities for ther-area and a degeneracy theorem forr-minimal graphs

We establish monotonicity inequalities for the r-area of a complete oriented properly immersed r-minimal hypersurface in Euclidean space under appropriate quasi-positivity assumptions on certain invariants of the immersion. The proofs are based on the corresponding first variational formula. As an application, we derive a degeneracy theorem for an entire r-minimal graph whose defining function ƒ has first and second derivatives decaying fast enough at infinity: Its Hessian operator D² ƒ has at least n − r null eigenvalues everywhere.     

The loss of tightness of time distributions for homeomorphisms of the circle

For a minimal circle homeomorphism we study convergence in law of rescaled hitting time point process of an interval of length 0$">. Although the point process in the natural time scale never converges in law, we study all possible limits under a subsequence. The new feature is the fact that, for rotation numbers of unbounded type, there is a sequence going to zero exhibiting coexistence of two non-trivial asymptotic limit point processes depending on the choice of time scales used when rescaling the point process. The phenomenon of loss of tightness of the first hitting time distribution is an indication of this coexistence behaviour. Moreover, tightness occurs if and only if the rotation number is of bounded type. Therefore tightness of time distributions is an intrinsic property of badly approximable irrational rotation numbers.

     

A linear semi-infinite programming strategy for constructing optimal wavelet transforms in multivariate calibration problems

A novel strategy for the optimization of wavelet transforms with respect to the statistics of the data set in multivariate calibration problems is proposed. The optimization follows a linear semi-infinite programming formulation, which does not display local maxima problems and can be reproducibly solved with modest computational effort. After the optimization, a variable selection algorithm is employed to choose a subset of wavelet coefficients with minimal collinearity. The selection allows the building of a calibration model by direct multiple linear regression on the wavelet coefficients. In an illustrative application involving the simultaneous determination of Mn, Mo, Cr, Ni, and Fe in steel samples by ICP-AES, the proposed strategy yielded more accurate predictions than PCR, PLS, and nonoptimized wavelet regression.