Central Adams operators

This is a supplement to our analysis [2] of Adams, or V₁, periodicity operators on mod p^a-Moore spaces using the J-map defined by a chosen solution of the Adams conjecture. Motivated by recent work of E. Devinatz, M. Hopkins and J. Smith, we use the same method to construct natural periodicity operators for arbitrary torsion spaces.     

Off-lattice Monte Carlo method with constraints: Long-time dynamics of a protein model without nonbonded interactions

A method is proposed to perform computer simulations of protein dynamics in the long-time regime. The method is based upon a Monte Carlo technique. The only molecular degrees of freedom considered are bond rotations. All other degrees of freedom including the amide plane torsions are kept rigid. These constraints approximately account for all interactions related to chemical bonding. An individual Monte Carlo step adopts the Go and Scheraga algorithm where local conformational changes in a small window of the protein backbone are performed. By using correlated rotations, the conformation of residues outside the window remains invariant. To test the reliability of the method, the nonbonded interactions are turned off in the present application. Exact statistical averages are compared with values obtained from data of computer simulation involving 2 × 10⁶ scans of the window along the protein backbone. Time is related to the number of scans of the window along the protein backbone. End-to-end distance autocorrelation functions decay to 1/e of its initial value in about 10³–10⁴ scans of the window algorithm. Time decay follows a stretched exponential Kohlrausch decay law. © 1993 John Wiley & Sons, Inc.     

EXAFS studies of nickel nafion ionomers

Nafion membranes neutralized with Ni²⁺ have been examined by extended x-ray absorption fine-structure (EXAFS) and x-ray absorption near-edge-structure (XANES) spectroscopy. The results indicate that in both the dry and water-soaked membranes, the nickel is in an octahedral site with six oxygen atoms as nearest neighbors. The degree of disorder in the Ni? O distance is comparable to that in ionic crystals in both the dry and hydrated materials. A contribution from a second shell of neighbors is very weak in the dry samples but, surprisingly, this contribution is strongly accentuated in the hydrated membranes. The data indicate that this contribution is due to neighboring Ni²⁺ cations. Thus the water absorption seems to enhance the local ordering of the cation environment. The local structure does not depend strongly on the concentration of ionic groups in the materials.     

Mass spectrometric size analysis of N2O-clusters

Mass spectra of N₂O-clusters in the size rangen?7,000 molecules per cluster, formed in a supersonic beam, have been recorded in a time-of-flight mass spectrometer. The spectra trace the transition from growth by successive monomer addition to growth by cluster coagulation. The influence of the ionization process and the detection probability is discussed.     

Influence of freezing of aqueous samples on the Fe(II)/Fe(III) equilibrium

The influence of freezing of aqueous samples on the Fe(II)/Fe(III) equilibrium has been investigated by ion chromatography. No change has been observed in the pH-range 2–5, irrespective of the freezing temperature.     

Decomposition methods in elemental trace analysis

Frequently, systematic errors in the decomposition step of a trace analytical multistage procedure lead to erroneous results in spite of the fact that expensive and powerful apparatus has been used for the determination. Of the numerous decomposition methods that have been published only a few meet the requirements of modern trace analysis.