Spingläser — einige typische physikalische eigenschaften und modelle

In this review-article we first present and discuss some typical physical properties of spin-glass-alloys, such as magnetic susceptibility, hysteresis, time-dependent magnetic effects, Mössbauer-spectrum, neutron magnetic scattering, specific heat and electrical conductivity. In the second part we discuss some attempts to understand the empirical properties of these systems on the background of model-calculations. Some of the existing theories explain the low-temperature-properties of spin-glasses on the basis of a magnetic phase transition (of third order), others consider the possibility of a peculiar magnetic freezing phenomenon. More exact measurements of specific heat in the critical temperature region should decide this question.     

Zwillingsbildung bei PolyÄthylen-Einkristallen

Zusammenfassung Bei der Kristallisation des PolyÄthylens aus der Lösung wachsen neben den rautenförmigen Einkristallen auch flügelartig ausgebildete Zwillingskristalle. Die Elektronenbeugung zeigt, da\ es sich bei unseren PrÄparaten um 110-Zwillinge handelt. Die seitlichen Begrenzungsebenen der flügelartigen Zwillingskristalle sind 110- bzw. 1¯10-Ebenen und liegen parallel zur 110-Zwillingsebene. Die Flügelenden sind hÄufig als geradlinige einspringende Ecken ausgebildet; die spitzen Winkel variieren von 67 bis ca. 90. Bei ausgezackten, nicht geradlinigen Flügelenden beobachteten wir wiederholt für kleinere Bereiche 110- bzw. 1¯10-Ebenen. Der Winkel von 67 wird wahrscheinlich dadurch zu höheren Werten verschoben, da\ in der einspringenden Ecke bevorzugt PolyÄthylen anwÄchst. Aus diesem bevorzugten Wachsen folgt auch die lÄngliche Gestalt der Zwillingskristalle.Herrn Professor Dr.K.-H. Hellwege danke ich für die Anregung zu dieser Arbeit, Herrn Dr.U. Johnsen für viele fördernde Diskussionen.     

Die Kaliumbestimmung in Milch

Ohne Zusammenfassung     

Size-dependent electron-impact detachment of internally cold Cn- and Aln- clusters

The cross sections for electron detachment of internally cold Cn- and Aln- clusters were measured using an electrostatic ion beam trap fitted with an internal electron target. The measured electron-impact detachment cross sections for the Cn- (n = 1-9) clusters exhibit even-odd oscillations reflecting the binding energy trend, namely, higher cross sections for weaker binding. Surprisingly, however, these cross sections increase on the average with cluster size, n, in spite of the increase in electron binding. In contrast, the Aln- (n = 2-5) clusters follow the known scaling laws for electron detachment. We suggest that the size-dependent polarizability of these clusters is responsible for the observed behavior.     

Deep UV laser induced fluorescence in fluoride thin films

Fluorescence experiments have been performed to study the interaction of 193-nm laser radiation with dielectric thin films of LaF₃, AlF₃, and MgF₂. Spectral- and time-resolved measurements reveal the presence of cerium in LaF₃ and the influence of hydrocarbons in MgF₂ and LaF₃. Virtually no fluorescence response is observable in the case of AlF₃. Supplementary measurements on multilayer stacks confirm the contribution of hydrocarbon and cerium emission in high-reflective UV mirrors upon ArF excimer laser irradiation. Energy density dependent measurements indicate a linear absorption process as the origin of UV laser induced fluorescence in LaF₃. Luminescence calculations are applied as a helpful tool in order to account for interference effects that are inherently to be found in the multilayer emission spectra. Received: 21 May 2002 / Accepted: 23 May 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +49-3641/807-601, E-mail: heber@iof.fraunhofer.de     

1H, 13C and 15N NMR spectral analysis of substituted 1,2,3,4‐tetrahydro‐pyrido[1,2‐a]pyrimidines

The NMR spectroscopic data of a series of thirty‐four 3‐acylpyrido[1,2‐a]pyrimidinium salts are analyzed, which were prepared as either perchlorates or chlorides. Methyl group substituted 3‐aroyltetrahydropyrido[1,2‐a]pyrimidines with the methyl substituent in positions 6, 8 and 9 as well as both in positions 6 and 8 were investigated bearing various aroyl substituents. Unequivocal assignment of all resonances was achieved via two‐dimensional ¹H,¹H‐COSY measurements, ¹H,¹³C and ¹H,¹⁵N HSQC as well as HMBC experiments, and important diagnostic CH and NH couplings in the heteroaromatic ring system are evaluated. The influence of the methyl substituents was analyzed on the proton, carbon and nitrogen shifts. A significant effect of the counter ion on some chemical shifts of the nuclei under discussion of the pyridopyrimidines is found, allowing the indirect detection of the anion, which is confirmed by direct measurement of the ³⁵Cl nucleus of the perchlorates. Copyright © 2013 John Wiley & Sons, Ltd.