Wave shapes in alternating DSC

ADSC with its periodical temperature programs combines the features of DSC measured at high heating rate (high sensitivity) with those at low heating rate (high temperature resolution). In addition, the “reversing” c_p effects can be separated from the “non-reversing” latent heat effects. Various periodical temperature programs can be applied. This paper compares the different possible temperature programs and their algorithms for the c_p determination for metal, metal oxide and polymer of various properties. Simulated and measured results for various wave shapes and samples are presented. The relevant sample properties and their influence on the measurements are identified and guiding rules for the proper choice of the various experimental parameters are given. Measurements with different samples, performed with the new METTLER TOLEDO STAR^e-System, are shown and compared with the simulation results. The simulations and the measurements clearly show that the alternating techniques can yield new information about sample properties, but are susceptible to the proper choice of the various experimental parameters.     

Tropyliumionen und tropilidene—V: Synthese und ambidente reaktivität von 7-chlor- und 7-brombenzocycloheptenyliumkationen

7H-Benzocyclohepten-7-one (1) reacts with oxalyl bromide to yield 7-bromobenzocycloheptenylium bromide (4a), a stable carbenium salt. In contrast, the reaction of oxalyl chloride or phosgene with 1 produces a covalent compound, 7,7-dichloro-7H-benzocycloheptent (3b), which ionizes in liquid sulfur dioxide to 7-chloro-benzocycloheptenylium chloride (4b). Nucleophiles are preferably added to C-5 ( C-9) of cation 4a; the resultant products are 7-bromo-5H-benzocycloheptenes (7b-h). The HMO model shows that the positive charge density in 4 is highest at C-5 ( C-9) thus favoring formation of addition products at this position under conditions of kinetic control. In those cases favorable to reversible addition, the competitive nucleophilic substitution at C-7 is the main reaction. The latter reaction occurs between 4a and ?-toluidine or N-methylaniline which produces 7-arylamino-benzocycloheptenylium bromides 13a,b. A further example is the hydrolysis of 4a and 3b to form 1.     

Towards measuring the ground state hyperfine splitting of antihydrogen – a progress report

We report the successful commissioning and testing of a dedicated field-ioniser chamber for measuring principal quantum number distributions in antihydrogen as part of the ASACUSA hyperfine spectroscopy apparatus. The new chamber is combined with a beam normalisation detector that consists of plastic scintillators and a retractable passivated implanted planar silicon (PIPS) detector.     

Experiences with the kinetical evaluation of calorimetric differential thermal analysis traces

Due to automatic computation the determination of kinetical data of chemical reactions is a routine today. Based on several years of experience in this field this paper shows — after a short introduction into the measuring principle — how to get reliable results and how to control arising difficulties.     

Progress in pion-decay channelling: Refractory bcc metals at high and low temperatures

By means of π⁺/μ⁺ channelling, positive pions (π⁺) implanted intoTa, Mo, andW are investigated up to high temperatures. A striking observation is that the channelling effect disappears in a rather narrow temperature interval centred at 0.26 (Ta) to 0.51 (W) of the melting temperature. From studies of π⁺ trapping by oxygen atoms inTa estimates for the low-temperature π⁺ diffusivity inTa [D _π(23K)=1.4·10^−10±0.3 m²s⁻¹,D _π(47K)=5.7·10^−10±0.3 m²s⁻¹] as well as for the binding enthalpy of π⁺ to 0 atoms (H _B=7·10⁻² eV) have been obtained. The diffusion data are in reasonable agreement with the theory of phonon-assisted tunnelling.     

Measuring Tollmien–Schlichting waves using phase-averaged particle image velocimetry

This article addresses the direct experimental measurement of Tollmien?CSchlichting waves on a flat plate, when the laminar boundary layer is excited by velocity perturbations; the free stream velocity was 16?m/s, the excitation frequency 250?Hz. The two-dimensional velocity field in proximity of the flat plate was captured using a conventional PIV system; however, the image recording was phase locked with the disturbance source and ensemble averaging was used to obtain characteristics of the Tollmien?CSchichting waves. In particular, after subtraction of the mean velocity, the characteristics of the excited waves in terms of streamlines were extracted, revealing that the investigated waves represented velocity deviations with an order of magnitude of 1?% of the undisturbed free stream flow. This study is a prelude to the use of the same technique to visualize the effect of dielectric barrier discharge plasma actuators on the suppression of such Tollmien?CSchlichting waves, which is difficult using other measurement techniques.     

First measurement of kaonic helium-3 X-rays

The first observation of the kaonic (3)He 3d→2p transition was made, using slow K- mesons stopped in a gaseous (3)He target. The kaonic atom X-rays were detected with large-area silicon drift detectors using the timing information of the K+K- pairs of ?-meson decays produced by the DAΦNE e+e- collider. The strong interaction shift of the kaonic (3)He 2p state was determined to be -2±2(stat)±4(syst) eV.