Strong-field molecular ionization: determination of ionization probabilities calibrated with field-free alignment

We report an original optical method providing the probability of molecular ionization induced by femtosecond laser pulses. The approach consists of exploiting molecular alignment to extract reliable information about ionization. The cross defocusing technique implemented for this purpose reveals a sensitivity with respect to postpulse alignment, as well as to the free electron density induced by the ultrashort laser pulse. The analysis of the resulting signal thus gives access to absolute single-ionization probabilities calibrated through the degree of alignment, provided that free electrons are produced mainly by single ionization. The relevance of the method is assessed in N2.     

Spatial confinement of ultrasonic force fields in microfluidic channels

We demonstrate and investigate multiple localized ultrasonic manipulation functions in series in microfluidic chips. The manipulation functions are based on spatially separated and confined ultrasonic primary radiation force fields, obtained by local matching of the resonance condition of the microfluidic channel. The channel segments are remotely actuated by the use of frequency-specific external transducers with refracting wedges placed on top of the chips. The force field in each channel segment is characterized by the use of micrometer-resolution particle image velocimetry (micro-PIV). The confinement of the ultrasonic fields during single- or dual-segment actuation, as well as the cross-talk between two adjacent fields, is characterized and quantified. Our results show that the field confinement typically scales with the acoustic wavelength, and that the cross-talk is insignificant between adjacent fields. The goal is to define design strategies for implementing several spatially separated ultrasonic manipulation functions in series for use in advanced particle or cell handling and processing applications. One such proof-of-concept application is demonstrated, where flow-through-mode operation of a chip with flow splitting elements is used for two-dimensional pre-alignment and addressable merging of particle tracks.     

Search for very light CP-odd Higgs Boson in radiative decays of Upsilon(1S)

We search for a non-SM-like CP-odd Higgs boson (a(1)(0)) decaying to tau(+)tau(-) or mu(+)mu(-) in radiative decays of the Upsilon(1S). No significant signal is found, and upper limits on the product branching ratios are set. Our tau(+)tau(-) results are almost 2 orders of magnitude more stringent than previous upper limits. Our data provide no evidence for a Higgs state with a mass of 214 MeV decaying to mu(+)mu(-), previously proposed as an explanation for 3 Sigma(+)-->pmu(+)mu(-) events observed by the HyperCP experiment. Our results constrain NMSSM models.     

Acoustic impedance matching of medical ultrasound transducers

Ultrasonic transducers for pulse-echo systems are studied both theoretically and experimentally. For the theoretical calculations the Mason model for thickness-mode disc transducers with and without backing and matching layers is used. By building several of the theoretically investigated transducer configurations it is shown that theory and experiment agree well. Thus the properties of a transducer can be predicted to a good approximation before its experimental realization. To find transducers with good sensitivity and short pulses, the pulse shape and frequency response for the following classes of transducers were studied both theoretically and experimentally: transducers with backing only, transducers with heavy backing and front matching layers, and air-backed transducers with front matching layers.     

Messung und Deutung des Leitwertabklingens zylindrischer Bögen

The decay of the electrical conductance of the column of a cascaded arc (100 A) after current interruption is measured for the gases N₂, SF₆, CO₂ and Ar. Numerical computations of temperature and conductance decay are in good agreement with experiment for Ar but for N₂ and SF₆ there are drastic deviations. An interpretation of the decay processes is given by the aid of a simple model for the energy transfer including nonequilibrium processes with regard to recombination in the wall near arc regions. Introducing the model by a formal manner in the computer program leads to good agreement with experiment.     

Determination electrochimique,par pile a electrolyte solide CaF2, des proprietes thermodynamiques de formation des alliages binaires (Ca,Cu) entre 800 et 1300 K

Thermodynamic quantities of formation of the CaCu system intermetallic phases are, for the first time, directly determined by means of electromotive force measurements. The alloy sample is prepared, in situ, on a copper point electrode by electrolysis. The activity of calcium in CaCu alloys is directly compared with that of pure calcium (liquid or solid) produced in the same conditions on an inert (iron) electrode.     

Die Struktur der ersten Hydrationssph?re von Ionen in Elektrolytl?sungen. Eine Untersuchung mit Hilfe der kernmagnetischen Relaxation

Ohne Zusammenfassung     

High-resolution spatial characterization of laser produced plasmas at soft x-ray wavelengths

In this article, we describe the setup and application of a system for the spatial characterization of laser-produced plasma x-ray sources. While pinhole cameras are normally used for this purpose, we employed a zone plate to act as the x-ray lens. Together with an x-ray CCD camera as the detector, a spatial resolution of up to 2 m was achieved. Due to the wavelength-dependent focal length of a zone plate, the monochromaticity of the image was better than /=150, and the large aperture of the zone plate allowed single-laser-shot images to be collected. Methanol and ethanol were used as liquid-jet target systems. Two different Nd:YAG lasers with pulse durations of 3 ns and 10 ns produced the plasmas. Our measurements concentrated on the line emission of carbon in the soft x-ray spectral range, namely, the hydrogen-like -line at 3.37 nm and the helium-like -line at 4.03 nm. We investigated the influence of different nozzle sizes, laser energies, and pulse durations on the source size of the plasma. Depending on the experimental conditions, plasma diameters of 17–60 m were measured. PACS 41.50.+h; 52.38.-r; 52.70.La     

Measurement of the decay constant f(Ds+) using D(s+)-->l+ nu

We measure the decay constant f(Ds+) using the D(s+)-->l+ nu channel, where the l+ designates either a mu+ or a tau+, when the tau+ -->pi+ nu. Using both measurements we find f(Ds+)=274+/-13+/-7 MeV. Combining with our previous determination of f(D+), we compute the ratio f(Ds+)/f(D+)=1.23+/-0.11+/-0.04. We compare with theoretical estimates.