A multiresolution space‐time adaptive scheme for the bidomain model in electrocardiology

The bidomain model of electrical activity of myocardial tissue consists of a possibly degenerate parabolic PDE coupled with an elliptic PDE for the transmembrane and extracellular potentials, respectively. This system of two scalar PDEs is supplemented by a time‐dependent ODE modeling the evolution of the gating variable. In the simpler subcase of the monodomain model, the elliptic PDE reduces to an algebraic equation. Since typical solutions of the bidomain and monodomain models exhibit wavefronts with steep gradients, we propose a finite volume scheme enriched by a fully adaptive multiresolution method, whose basic purpose is to concentrate computational effort on zones of strong variation of the solution. Time adaptivity is achieved by two alternative devices, namely locally varying time stepping and a Runge‐Kutta‐Fehlberg‐type adaptive time integration. A series of numerical examples demonstrates that these methods are efficient and sufficiently accurate to simulate the electrical activity in myocardial tissue with affordable effort. In addition, the optimal choice of the threshold for discarding nonsignificant information in the multiresolution representation of the solution is addressed, and the numerical efficiency and accuracy of the method is measured in terms of CPU time speed‐up, memory compression, and errors in different norms. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010     

On correlations between charged and neutral particles in a cluster model

Correlations between charged and neutral pions at high energies are investigated in the framework of a cluster model in which neutral clusters have a decay distribution determined by isospin conservation and statistical independence. For 〈n₀〉_n? an asymptotic expansion around the mean 〈n_?〉 leading asymptotically to a quadratic form in n_? is derived and compared with data.     

Analysis of human tear proteins by different high-performance liquid chromatographic techniques

A comparison of the efficiencies of hydrophobic interaction chromatography, ion-exchange chromatography, reversed-phase chromatography and gel permeation chromatography in the separation of tear proteins was made using a variety of different buffers. Separation of immunoglobulins, lactoferrin, albumin, PMFA (protein migrating faster than albumin) and lysozyme was accomplished by gel permeation chromatography in less than 30 min using a TSK-type SW3000 column equilibrated with ammonium acetate buffer (pH 4.1) with a high reproducibility. When gel permeation chromatography was used as a completely automated diagnostic method, only minute volumes (1.0 microliter) of tear samples were necessary for the quantitative analysis of proteins. The other three methods proved to be more suitable for the preparation of individual tear proteins but were less suitable for their quantitation.     

Factors influencing the C-O bond homolysis of alkoxyamines: effects of H-bonding and polar substituents

The synthesis of various new trialkylhydroxylamines is described. The rate constant of the C-O bond cleavage of these new alkoxyamines has been measured. For example, C-O bond homolysis rates in a series of para-substituted TEMPO-styryl compounds TEMPO-CH(CH3)C6H5X 1a (p-MeO), 1b (p-Me), 1d (p-H), 1e (p-Br), and 1f (p-MeO2C) are presented. Furthermore, rate constants for the C-O bond cleavage of alpha-heteroaryl-substituted secondary alkoxyamines are discussed. A correlation by which the rate constant for the C-O bond cleavage of TEMPO-derived alkoxyamines can be predicted from the C-H BDEs of the corresponding alkanes is presented. Solvent effects as well as the effect of camphorsulfonic acid on the rate of the C-O bond homolysis are discussed. Finally, EPR and kinetic evidence show that alkoxyamines derived from nitroxides which are capable of intramolecular H-bonding undergo C-O bond cleavage faster than the corresponding non-H-bond-forming analogues.     

Über die 2-(1,2,3,4-Tetrahydro-4,4,6-trimethyl-2-thioxopyrimidin-1)-benzoesäure und das 2,3,4,4a-Tetrahydro-3,3,4a-trimethyl-1-thioxo-1H, 6H—pyrimido[1,6-a][3,1]-benzoxazin-6-on Über Heterocyclen, 55. Mitt.

Dimethyloxobutylisothiocyanate1 reacts with anthranilic acid to a mixture of much pyrimidobenzoxazine5 a and less tetrahydrothioxopyrimidinebenzoic acid3 a (and tautom.4 a resp.). By treatment with methanolic KOH solution5 a is converted into3 a, 4 a. At refluxing temperature3 a, 4 a, and5 a resp., are rearranged inDMF into thioxopyridineanthranilic acid7 a, thioxopyridineanthranilic dimethylamide7 d and dimethylaminodihydro-2(1H)-pyridinethione8. Also pyridineanthranilates7b, c and pyridineanthranilic nitrile12 are formed from pyrimidinebenzoic esters3 b, 4 b, 3 c, 4 c and pyrimidinebenzoic nitrile10, 11 resp., by boiling inDMF. The reaction of1 with methyl anthranilate leads to7 b and triazapentaphene9. o-Aminobenzoic nitrile HCl reacts with1 to pyrimidinequinazoline5 b.     

Comprehensive two-dimensional gas chromatography coupled to a rapid-scanning quadrupole mass spectrometer: principles and applications

The principles, practicability and potential of comprehensive two-dimensional (2D) gas chromatography coupled to a rapid-scanning quadrupole mass spectrometer (GC x GC-qMS) for the analysis of complex flavour mixtures in food, allergens in fragrances and polychlorinated biphenyls (PCBs) were studied. With a scan speed of 10,000 amu/s, monitoring over a mass range of up to 200 atomic mass unit (amu) can be achieved at an acquisition frequency of 33 Hz. Extending this mass range and/or increasing the data acquisition frequency results in a loss of spectral quality. Optimal parameter settings allow, next to unambiguous identification/confirmation of target compounds on the basis of high-quality mass spectra, fully satisfactory quantification (three to four modulations per peak) with linear calibration plots and detection limits in the low-pg level. The potential of time-scheduled data acquisition to increase the effective mass range within one GC x GC run was also explored. The analyses, with baseline separation of the flavours, allergens and PCB target compounds, took less than 30 min.