Anwendung von mathematischen statistischen methoden für einige probleme der quantitativen emissionsspektralanalyse

The standard deviation of the ΔY-values of an analytical line pair is discussed in function of the correlation and orthogonal regression coefficients as well as of the standard deviations of Y_x and Y_r.

It was stated that the orthogonal regression coefficient depends on the ratio s_x/s_r.

A criterium is set up for choosing the right analytical line pair. The optimal field for the values ^sδy is given in function of the ratio s_x/s_r as well as of the correlation coefficient.     

Disordered Magnetic Phase in Partially Oxidized Bulk Nanocrystalline Iron

Magnetically frozen partially disordered state was observed in nanocrystalline bulk iron prepared by ball-milling of microcrystalline Fe. Role of nanostructure and oxidized fraction is pointed out. Altough we have found a small constituent which is proportional to 1/T in the ZFC curve, the magnetization scaling with T ^3/2 at high fields and the hysteretic behavior in FC-ZFC curves signalizes the presence of frozen ferromagnet at low temperatures.     

Flocculation of cellulose fibres: new comparison of crowding factor with percolation and effective-medium theories

New comparisons of percolation and effective-medium theories on one hand, and predictions from the crowding factor on the other hand, are described for calculating critical concentrations in suspensions of cellulose fibres. The connectivity threshold from percolation theory appears to correspond to the “gel crowding factor”, which occurs at crowding factor (N) of N = 16 rather the criterion for fibre collisions, N = 1, postulated in earlier work. The rigidity threshold from percolation theory corresponds to the onset of coherent fibre flocs having mechanical network strength, which occurs at about N = 60. The latter value exceeds the gel crowding factor value by a factor of 3.75. In comparison, percolation theory predicts that flocculation occurs at a rigidity concentration four times higher than the connectivity threshold. These ratios are in good agreement.     

Kinetic analysis of TG data XXXVI: Influence of procedural variables upon the apparent kinetic parameters of the thermal deamination

A number of 7 complexes of the [Co(DH)₂(amine)₂)]I type (DH₂ stands for dimethyloxime) have been studied by means of thermogravimetry and differential scanning calorimetry in nitrogen atmosphere, by using heating rates of 2.5, 5 and 10 K min^–1. In all cases an endothermal deamination reaction occurs leading to the relatively stable [Co(DH)₂I(amine)] intermediate. For this reaction apparent kinetic parameters have been derived. The influence of heating rate is discussed. The validity of a linear and a non-linear kinetic compensation law was verified.This revised version was published online in November 2005 with corrections to the Cover Date.     

The effects causing the burning of plastic coatings of fire-resistant cables and its consequences

Journal of Thermal Analysis and Calorimetry - Electric wiring is part of the fire protection systems; therefore, it must work reliably for a given period of time. Cable is in the first place among...     

Effect of thermal transformation and stability on the flammability of PAN precursors-based carbon fibres

Journal of Thermal Analysis and Calorimetry - During the development of the carbon fibres and oxidized fibres, the aim was to get a material with extraordinary mechanical properties. Nowadays, it...     

Equilibrium and structure of the Al(III)-ethylenediamine-N,N'-bis(3-hydroxy-2-propionate) (EDBHP) complex. A multi-method study by potentiometry, NMR, ESI MS and X-ray diffraction

The equilibrium and structure of the complex formed by Al(III) and ethylenediamine-N,N'-bis(3-hydroxy-2-propionate) (EDBHP2-) have been studied using pH-potentiometry, 1H and 27Al NMR, ESI MS and single crystal X-ray diffraction methods. The EDBHP ligand is a strong Al-binder in aqueous solution for pH between 4 and 8 and for c(Al) = c(EDBHP)> or = 0.1 mmol dm(-3). The dominating complex identified by ESI MS and potentiometry is a neutral dimer, Al2L2(OH)2, with logbeta(22-2) = 14.16 +/- 0.03. In the solid Al2(EDBHP)2(OH)2.2H2O the Al(III) ions are connected through a double hydroxo bridge. Both four-dentate organic ligands are coordinated terminally through two carboxylate groups and two N-donors forming three five-membered chelate rings. The hydroxyl groups of the ligand EDBHP remain protonated and are not coordinated to the aluminium ions. The structure and composition of the dimer are very likely the same in solution and the solid state.     

Esters of 1-O-Demethylthiocolchicines: Formation of Isomers in Chloroform Solution

1-O-Acetyl-1-O-demethylcolchicine, and acylated 1-O,2-O-didemethylthiocolchicines, in contrast to 2-O-acetyl-, 2-O,3-O-diacetyl- and 3-O-acetyl analogs, showed after standing in CHCl₃ solution significant changes in optical rotation, a duplication of ¹H-NMR signals, and the formation of new isomers on TLC. Solid-state X-ray diffraction of O-acetylated colchinoids and thio analogs, showed out of planar arrangements of the aromatic substituents, but the analysis could not help to explain the structures of the newly formed isomers in CHCl₃ solution.     

An allenic Pauson-Khand-type reaction: a reversal in pi-bond selectivity and the formation of seven-membered rings

[reaction: see text] Treatment of alkynyl allenes with [Rh(CO)(2)Cl](2) results in a formal [2 + 2 + 1] cycloaddition reaction. This reaction occurs with complete regioselectivity for a variety of substrates affording only 4-alkylidene cyclopentenones in good yields. Moreover, seven-membered rings have been prepared in high yields.