Fresnel diffraction mirror for an atomic wave

We have experimentally demonstrated a material-independent mirror for atomic waves that uses the Fresnel diffraction at an array of parallel ridges. He* (2 (3)S(1)) and Ne* (1s(3)) atomic waves were reflected coherently on a silicon plate with a microfabricated grating structure, consisting of narrow wall-like ridges. We measured the reflectivity at grazing incidence as a function of the incident velocity and angle. Our data show that the reflectivity on this type of mirror depends only on the distance between the ridges, the wavelength, and the incident angle, but is insensitive to the material of the grating structure. The reflectivity is observed to increase by 2 orders of magnitude, compared to that of a flat polished silicon surface, where the reflection is caused by the attractive surface potential. For He* atoms, the measured reflectivity exceeds 10% for normal incident velocities below about 25 cm/s.     

Diode laser spectrometer at 493 nm for single trapped Ba+ ions

+ ions. Frequency doubling of a 100 mW diode laser at 986 nm results in up to 60 mW output power at 493 nm in a bandwidth of less than 60 kHz with respect to the cavity used for locking. Reference frequencies of 18 spectral lines of Te₂ near the 493 nm resonance of Ba⁺ have been measured using modulation transfer spectroscopy. The fluorescence excitation spectrum of a single Ba⁺ ion, measured with this laser, exhibits well-resolved dark resonances, which confirms the versatility of the system for quantum optical experiments. Received: 12 June 1998     

Chaos in brake squeal noise

Brake squeal has become an increasing concern to the automotive industry because of warranty costs and the requirement for continued interior vehicle noise reduction. Most research has been directed to either analytical and experimental studies of brake squeal mechanisms or the prediction of brake squeal propensity using finite element methods. By comparison, there is a lack of systematic analysis of brake squeal data obtained from a noise dynamometer. It is well known that brake squeal is a nonlinear transient phenomenon and a number of studies using analytical and experimental models of brake systems (e.g., pin-on-disc) indicate that it could be treated as a chaotic phenomenon. Data obtained from a full brake system on a noise dynamometer were examined with nonlinear analysis techniques. The application of recurrence plots reveals chaotic structures even in noisy data from the squealing events. By separating the time series into different regimes, lower dimensional attractors are isolated and quantified by dynamic invariants such as correlation dimension estimates or Lyapunov exponents. Further analysis of the recurrence plot of squealing events by means of recurrence quantification analysis measures reveals different regimes of laminar and random behaviour, periodicity and chaos-forming recurrent transitions. These results help to classify brake squeal mechanisms and to enhance understanding of friction-related noise phenomena.     

Efficient coherent population transfer among three states in NO molecules by Stark-Chirped rapid adiabatic passage

We present the experimental demonstration of a novel, efficient, and selective technique to prepare population inversion. The technique is an extension of Stark-chirped rapid adiabatic passage (SCRAP), i.e., SCRAP among three states. In this process a Lambda-type quantum system is driven by two laser pulses, the pump and Stokes pulses, which are appropriately detuned from transition frequencies. A third laser pulse induces a dynamic Stark shift in the upper energy level, and the timing of all three pulses is controlled in order to prepare population inversion between the two lower states in the Lambda-type level scheme. Our data on population transfer in nitric oxide (NO) molecules clearly show that SCRAP among three states provides an advantageous alternative to such techniques as stimulated Raman adiabatic passage.     

Basiserweiterung in der Homologie kleiner Kategorien

Ohne ZusammenfassungGeschrieben mit Unterstützung von NSF-grant GP-5870.     

Schwingungsdämpfende Kunststoffe aus optimal eingestellten Polymeren

Ohne Zusammenfassung Herrn Prof. Dr. F. H. Müller zum 60. Geburtstag gewidmet.     

Influence of molecular relaxation processes on mechanical properties of polyvinyl chloride in tensile experiments

The relation between the molecular relaxation processes and the results of tensile experiments has been studied for hard and toughened polyvinyl chloride (PVC). The relaxation spectra have been determined between 10^?4 and 10⁺⁴ sec by means of stress relaxation, flexural vibration experiments, and tensile tests. Yield stress, yield strain, rupture stress, rupture strain, and rupture energy have been determined at 23° and 50° C as functions of yield time or rupture time, respectively, over a time-range from 10^?2 to 10⁺⁴ sec approximately. It is shown that the molecular relaxation processes observed in the range of small deformations also influence the behavior in the nonlinear range, especially the elongation at rupture in tensile experiments. In addition, effects of the molecular processes on the yield stress, the rupture stress, and, consequently, the rupture energy have been observed. These effects are due to the time- and temperature-dependent decrease of the macroscopic stress and of the microscopic notch stresses by certain relaxation mechanisms. The most suitable characteristic parameters in tensile experiments are the yield stress and the rupture strain. It is pointed out that the usefulness of a single value of a mechanical property as determined in a standard “one-point” test is very restricted.     

New colour reagents for the analysis of alkylating agents

Summary The sensitivity of the colour reaction between PBH (4-pyridinealdehyde-1-benzothiazolyl hydrazone) and alkylating agents is limited by inevitable side reactions of varying intensity. Therefore the photometric determination of alkylating agents at 500 nm is disturbed by background colouring. Three new colour reagents PPH (4-pyridinealdehyde-1-phthalazolyl hydrazone), PXH (4-pyridinealdehyde-4-carboxy-phenyl hydrazone) and PQH (4-pyridinealdehyde-isonicotinic acid hydrazide) were synthesized and tested for their ability to determine traces of alkylating agents. The results were compared with data obtained from the reaction with PBH. Although the molar extinction coefficients of the reaction between PPH, PQH and PXH and alkylating agents are normally lower compared to PBH, the detection limit is decreased due to the fact that side reactions can be eliminated nearly completely.

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Neue Farbreagentien für die Bestimmung von Alkylantien

     

Motional sidebands and direct measurement of the cooling rate in the resonance fluorescence of a single trapped ion

Resonance fluorescence of a single trapped ion is spectrally analyzed using a heterodyne technique. Motional sidebands due to the oscillation of the ion in the harmonic trap potential are observed in the fluorescence spectrum. From the width of the sidebands the cooling rate is obtained and found to be in agreement with the theoretical prediction.