Mass spectrometric behavior of levoglucosan under different ionization conditions and implications for studies of cellulose pyrolysis

Pyrolysis-mass spectrometric studies of cellulose indicate low abundances of levoglucosan in the product spectrum compared to the yield values determined in more conventional types of pyrolysis studies. To examine the reason for these conflicting observation, levoglucosan was examined under different ion source conditions and ionization modes to ascertain the relative contributions of thermal degradation and ionization fragmention to the low abundances of the levoglucosan molecular ion. Low-energy electron ionization using conventional sample volatilization and molecular-beam sampling is compared to chemical ionization using methane, isobutane, and ammonia as reagent gases, and to field ionization and desorption. The mass spectrometric fragmentation patterns under the various systems indicate that studies of cellulose pyrolysis underestimate the amount of levoglucosan formed due to ionization fragmentation and thermal rearrangement reactions in the ion source. Several peaks, including m/z 126 and 144, are dominated by the contribution from the fragmentation of levoglucosan.     

Intermolecular interactions of polymethacrylic acid with nonylphenoxypoly(ethoxy)ethanol in water solutions

On the basis of concentration pH dependences of binary solutions of anionic polyelectrolyte, polymethacrylic acid, and nonionic surfactant, nonylphenoxypoly(ethoxy)ethanol the role of hydrophobic interaction in the development of associative and aggregative processes was shown. It is established that the criterion of evaluation of the preferred contribution of hydrophobic interaction is the inflection point on the dependence of pH difference of the individual solutions of nonylphenoxypoly(ethoxy)ethanol and binary solutions of polymethacrylic acid and nonylphenoxypoly(ehoxy)ethanol on the logarithm of ratio of their concentrations.     

On the Ehrenfeucht–Mycielski sequence

We introduce the inverted prefix tries (a variation of suffix tries) as a convenient formalism for stating and proving properties of the Ehrenfeucht–Mycielski sequence [A. Ehrenfeucht, J. Mycielski, A pseudorandom sequence—how random is it? American Mathematical Monthly 99 (1992) 373-375]. We also prove an upper bound on the position in the sequence by which all strings of a given length will have appeared; our bound is given by the Ackermann function, which, in light of experimental data, may be a gross over-estimate. Still, it is the best explicitly known upper bound at the moment. Finally, we show how to compute the next bit in the sequence in a constant number of operations.     

Verschiedene Ger?te

Ohne Zusammenfassung     

Referate

Ohne Zusammenfassung     

Proving properties of matrices over {\mathbb{Z}_{2}}

We prove assorted properties of matrices over ${\mathbb{Z}_{2}}$ , and outline the complexity of the concepts required to prove these properties. The goal of this line of research is to establish the proof complexity of matrix algebra. It also presents a different approach to linear algebra: one that is formal, consisting in algebraic manipulations according to the axioms of a ring, rather than the traditional semantic approach via linear transformations.