Quantum Brownian Motion. II

This paper generalizes some previous resultspresented in Gaioli et al. [Int. J. Theor. Phys. 36,2167 (1997)]. We evaluate the autocorrelation functionof the stochastic acceleration and study the asymptotic evolution of the mean occupation number of aharmonic oscillator playing the role of a Brownianparticle. We also analyze some deviations from the Bosepopulation at low temperatures and compare it with the deviations from the exponential decay lawof an unstable quantum system.     

Corrections to scaling for diffusion exponents on three-dimensional percolation systems at criticality

Recent results of Monte Carlo simulations of the ant-in-the-labyrinth method in three-dimensional percolation lattices are reanalyzed in the light of more accurate corrections to scaling ansatz, motivated by inconsistent results that have appeared in the literature. The results are observed to be sensitive to the form of the scaling correction terms. Using a single correction term, we estimate the valuek=0.197±0.004 for the anomalous diffusion exponent at criticality. When two correction terms are included,k=0.200±0.002 is obtained. These new estimates are consistent with known theoretical bounds, with recent series expansion results, and with numerical calculations of the conductance of random resistor networks above criticality.     

Characterization of diazeniumdiolate nitric oxide donors (NONOates) by electrospray ionization mass spectrometry

Diazeniumdiolates (also called NONOates) have been analyzed by electrospray ionization mass spectrometry (ESI-MS). The samples used are commercially available and included Diethylamine NONOate, DETA NONOate, Spermine NONOate, MAHMA NONOate, PROLI NONOate, Dipropylenetriamine NONOate, PAPA NONOate, and Sulpho NONOate. These compounds have been found to ionize upon ESI by protonation, deprotonation and sodiation. The MS(n) experiments provided strong evidence that such ions release NO, HNO, N(2)O, NO(2), N(2)O(2), N(3)O(3), N(4)O(3) and N(4)O(4) when collisionally activated. Thus, the facile donation of NO units is a property of such compounds. Negative-mode mass spectrometry has been particularly useful for the analysis of most of the NONOates studied here. The experiments have demonstrated the capabilities of mass spectrometry, along with CAD (MS/MS), to detect and characterize such compounds.     

Characterization of polyethylenimine by electrospray ionization and matrix-assisted laser desorption/ionization

Branched polyethylenimines (PEIs) with lower average molecular weights (600, 1200 and 1800 Da) have been studied by Electrospray Ionization (ESI) and Matrix‐Assisted Laser Desorption/Ionization (MALDI) mass spectrometry. In both, ESI and MALDI mass spectra, the main distribution arises from protonated PEI oligomers with NH₂ end groups, [PEI + H]⁺, which are observed at m/z 43n + 18. A trace of sodium contamination in the PEI samples results in the presence of a series that appears at m/z 43n + 40 [PEI + Na]⁺. However, only the MALDI mass spectra show a [PEI + K]⁺ series at m/z 43n + 56, because of matrix contamination with potassium, and a series generated by condensation of the matrix with PEI at m/z 43n + 30. Collisionally activated dissociation tandem mass spectrometry (CAD (MS/MS)) of protonated PEI oligomers is shown to yield three fragment ion series b_n, and K_n. The experiments have demonstrated the capabilities of these mass spectrometry techniques, along with CAD MS/MS to detect and characterize such polar synthetic polymers. Copyright © 2011 John Wiley & Sons, Ltd.     

On a Helly-type question for central symmetry

Periodica Mathematica Hungarica - We study a certain Helly-type question by Konrad Swanepoel. Assume that X is a set of points such that every k-subset of X is in centrally symmetric convex...