Asynchronous sampling for ultrafast experiments with low momentum compaction at the ANKA ring

A high‐repetition‐rate pump–probe experiment is presented, based on the asynchronous sampling approach. The low‐α mode at the synchrotron ANKA can be used for a time resolution down to the picosecond limit for the time‐domain sampling of the coherent THz emission as well as for hard X‐ray pump–probe experiments, which probe structural dynamics in the condensed phase. It is shown that a synchronization of better than 1 ps is achieved, and examples of phonon dynamics of semiconductors are presented.     

Spring-block approach for crack patterns in glass

Fracture patterns resulting from point-like impact acting perpendicularly on the plane of a commercial sodalime glass plate is modelled by a spring-block system. The characteristic patterns consist of crack lines that are spreading radially from the impact point and concentric arcs intersecting these radial lines. Experimental results suggest that the number of radial crack lines is scaling linearly with the energy dissipated during the crack formation process. The elaborated spring-block model reproduces with success the observed fracture patterns and scaling law.     

Laser ultrasonics in copy paper: bending stiffness dependence on temperature and moisture content

The A0 Lamb mode in copy paper is generated and detected by using laser ultrasonics. The frequency dependence of the group velocity of the A0 mode is found from the wavelet transform of the measured signal. A best fit of the dispersion curve against predictions based on orthotropic plate theory yields an estimate of the bending stiffness of the sample. The sample is enclosed in an environmental chamber so that the effects of temperature and humidity can be controlled. Results indicate that the bending stiffness decreases with increasing temperature at an approximate rate of 4 x 10(-6) N m/degrees C, and that it decreases with increasing percent moisture content (PMC) at an approximate rate of 2 x 10(-5) (N m)/PMC.     

An unprecedented surface oxidation of polystyrene substrates by wet chemistry under basic conditions

The surface of polystyrene substrates has been modified by wet chemistry consisting of a treatment with sodium hydroxide in a water-methanol solution at 50 degrees C for 15 h, under air atmosphere. The resulting samples were analyzed by XPS and AFM. The surface functional groups (hydroxyl and carboxyl functions) were assayed by radiolabeling. All the results are consistent with a surface oxidation process.     

Gas-phase behaviour of negative ions produced from thiazidic diuretics under electrospray conditions

A systematic mass spectrometric study of 10 thiazidic diuretics and related compounds was undertaken by mass spectrometry (MS) with electrospray ionization in the negative ion mode. Collisional dissociation 'in-source' (CID-MS) and in a low-pressure collision cell (CID-MS/MS) were compared in both excitation regions. Spectra obtained by CID-MS and by CID-MS/MS were matched. Using the two methods, loss of HCl and consecutive dissociations from 2HCl losses were exhibited from compounds such as methyclothiazide and trichlormethiazide but not from other thiazidic diuretics that contain chlorine substituents in the aromatic moiety. However, deprotonated dichlorphenamide gave rise to loss of HCl by CID-MS and CID-MS/MS. For other diuretics such as hydroflumethiazide and hydrochlorothiazide, the loss of HCN and [HCN + SO(2)] was relevant. Reaction mechanisms were checked by means of deuterium-hydrogen exchange, which showed that deprotonation took place regioselectively on the heterocyclic moiety. The cleavage pathways require molecular isomerization forming ion-dipole complexes prior to decompositions, allowing long-distance proton transfer for neutral elimination. Identifications of the most specific fragmentations presented in this paper were applied to the screening and unambiguous identification of diuretics for horse doping control.     

Dialkylzinc-assisted alkynylation of nitrones

[reaction: see text]. Reaction of nitrones with terminal alkynes takes place readily in the presence of a substoichiometric amount of diethylzinc in toluene, affording N-propargyl-hydroxylamines in excellent yields and purity.     

Air-dispersion measurement by second-harmonic heterodyne interferometry

Interferometers with long optical paths in air usually require knowledge and control of air dispersion. In addition, the measurements at several wavelengths and the dispersion properties of air allow errors caused by air turbulence to be compensated for. An innovative technique for air-dispersion measurement is described for long-baseline ground-based stellar interferometers. The technique combines second-harmonic interferometry and heterodyne detection to permit high-resolution measurement even for low optical powers. Experimental results show measurements of air dispersion in good agreement with the values predicted from the Edlén equation.     

Reaction of lithium dimethylcuprate with conformationally biased β-acyloxy enol esters - regio and stereocontrolled access to functionalized six-carbon chiral synthons

Alkyl 2-acyloxy α-D-erythro-hex-2-enopyranoside diesters, readily available from D-hexoses, are versatile intermediates fro the expeditious preparation of six-carbon chiral synthons containing alternating and/or consecutive C-methyl and hydroxyl groups.