Electron beam moiré

A method of writing very high frequency line and dot pattems, in excess of 10,000 lines/mm, is described. This method uses a very small diameter, 10 to 20 nm, beam of electrons to sensitize a 100-nm thick layer of electron resist. The line and dot patterns are produced by etching the sensitized resist. Moiré fringe patterns occur when the line arrays are observed in the scanning electron microscope. Moiré fringes with excellent contrast have been produced at magnifications as high as 1900x. This capability permits e-beam moiré to be employed in micromechanics. Examples of line arrays, dot arrays and moiré fringe patterns on a brass disk and on a tensile specimen fabricated from glass-fiber-reinforced plastic are demonstrated to introduce the possibilities for micromechanics applications.     

The pion radius

The pion radius has been measured by direct scattering of 50 GeV negative pions from stationary electrons in a hydrogen target. We find the square of the radius to be 〈r_π²〉 = (0.61 ± 0.15)fm².     

Hochaufl?sende NMR an L?sungen mit Nitroxidradikalkomplexen

Ohne Zusammenfassung     

Influence of late-breaking ligaments on crack propagation in compact specimens—A photoelastic study

Dynamic photoelasticity and high-speed photography were utilized to study the influence of tough ligaments on crack propagation in compact specimens. The data obtained during the fracture experiments were analyzed to obtain crack velocity, instantaneous stress-intensity factor and the energy losses away from the crack tip. The results showed that the ligaments can behave as crack arrestors or decelerators. The crack if not arrested at the ligament slowly tunnels in between the ligaments without immediately rupturing them. The ligaments also tend to increase damping losses in the specimens.     

On the fidelity of high-speed photographic systems for dynamic photoelasticity

A general theory has been developed which predicts the influence of the characteristics of a high-speed recording system on the fidelity of a dynamic photoelastic-fringe pattern. The general theory was applied to recording systems currently employed in dynamic photoelasticity which include the high-speed framing camera, the spark-gap camera and the Q-spoiled laser system. Equations for a nondimensional form of the exposure as a function of normalized position have been developed for each of these three recording systems. From these equations, criteria to measure the fidelity of the recording systems were established. The methods developed are applied to the spark-gap system and examples of resolution limits, time shift and distortion are illustrated.     

Assessment of interferences to nonlinear two-line atomic fluorescence (NTLAF) in sooty flames

Nonlinear excitation regime two-line atomic fluorescence (NTLAF) is a laser-based thermometry technique that has application in turbulent flames with soot. However, no assessment of the various interferences from soot or its precursors in flames with high soot loadings on the technique is available. To examine these issues, both on- and off-wavelength NTLAF measurements are presented and compared for laminar nonpremixed ethylene-air flames. Laser-induced incandescence (LII) measurements were used to determine the corresponding soot concentration and location in the investigated flames. The measurements indicate that interferences, such as spurious scattering and laser-induced incandescence from soot, are not significant for the present set of flame conditions. However, interferences from soot precursors, predominantly condensed species (CS) and perhaps polycyclic aromatic hydrocarbons (PAH), can be significant. Potential detection schemes to correct or circumvent these interference issues are also presented.     

Photodesorption of alkali anions from alkali-halide cluster anions

Using photoelectron spectroscopy, we have observed alkali anion photodesorption from alkali-halide cluster anions that contain two weakly bound electrons. In the alkali iodides, we have found this type of desorption in almost every (MI)(n)M- cluster we have studied (M=Na, K, Cs; n<9), although it depends on the probe laser frequency and cluster temperature. Using pump-probe techniques, we have shown that the process occurs on a picosecond time scale by way of an electronic excitation of the cluster's spin-paired electrons.