Evolution of shock-accelerated heavy gas layer

The evolution of an $\text{SF}_{6}$ layer surrounded by air is experimentally studied in a semi-annular convergent shock tube by high-speed schlieren photography. The gas layer with a sinusoidal outer interface and a circular inner interface is realized by the soap-film technique such that the initial condition is well controlled. Results show that the thicker the gas layer, the weaker the interface–coupling effect and the slower the evolution of the outer interface. Induced by the distorted transmitted shock and the interface coupling, the inner interface exhibits a slow perturbation growth which can be largely suppressed by reducing the layer thickness. After the reshock, the inner perturbation increases linearly at a growth rate independent of the initial layer thickness as well as of the outer perturbation amplitude and wavelength, and the growth rate can be well predicted by the model of Mikaelian (Physica D, vol. 36, 1989, pp. 343–357) with an empirical coefficient of 0.31. After the linear stage, the growth rate decreases continuously, and finally the perturbation freezes at a constant amplitude caused by the successive stagnation of spikes and bubbles. The convergent geometry constraint as well as the very weak compressibility at late stages are responsible for this instability freeze-out.

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Simple Identification of Electron Diffraction Ring Patterns

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100062713 ◽

1969 ◽

Vol 27 ◽

pp. 160-161

Author(s):

Carolyn Nohr ◽

Ann Ayres

Keyword(s):

Electron Microscope ◽

Electron Diffraction ◽

Diffraction Ring ◽

Image Position

Texts on electron diffraction recommend that the camera constant of the electron microscope be determine d by calibration with a standard crystalline specimen, using the equation

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Atomic orientation effects in proton stopping at low velocity

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100077116 ◽

1983 ◽

Vol 41 ◽

pp. 708-709

Author(s):

Kin Lam

Keyword(s):

Polycrystalline Material ◽

Charged Particles ◽

Target Material ◽

Stopping Power ◽

Low Velocity ◽

Electronic Density ◽

Interatomic Distances ◽

Frame Work ◽

Image Position ◽

Atomic Orientation

The energy of moving ions in solid is dependent on the electronic density as well as the atomic structural properties of the target material. These factors contribute to the observable effects in polycrystalline material using the scanning ion microscope. Here we outline a method to investigate the dependence of low velocity proton stopping on interatomic distances and orientations.The interaction of charged particles with atoms in the frame work of the Fermi gas model was proposed by Lindhard. For a system of atoms, the electronic Lindhard stopping power can be generalized to the formwhere the stopping power function is defined as

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A Magnetic Spectrometer for a Scanning Transmission Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052195 ◽

1974 ◽

Vol 32 ◽

pp. 436-437

Author(s):

A. Kosiara ◽

J. W. Wiggins ◽

M. Beer

Keyword(s):

Scanning Transmission Electron Microscope ◽

Magnetic Spectrometer ◽

Fringe Field ◽

Curvature Radius ◽

Magnetic Pole ◽

Quadrupole Field ◽

Transmission Electron ◽

Scanning Transmission ◽

Under Construction ◽

Image Position

A magnetic spectrometer to be attached to the Johns Hopkins S. T. E. M. is under construction. Its main purpose will be to investigate electron interactions with biological molecules in the energy range of 40 KeV to 100 KeV. The spectrometer is of the type described by Kerwin and by Crewe Its magnetic pole boundary is given by the equationwhere R is the electron curvature radius. In our case, R = 15 cm. The electron beam will be deflected by an angle of 90°. The distance between the electron source and the pole boundary will be 30 cm. A linear fringe field will be generated by a quadrupole field arrangement. This is accomplished by a grounded mirror plate and a 45° taper of the magnetic pole.

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Optimizing conditions for x-ray microchemical analysis in analytical electron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109884 ◽

1978 ◽

Vol 36 (1) ◽

pp. 548-549 ◽

Cited By ~ 2

Author(s):

N. J. Zaluzec

Keyword(s):

Solid Angle ◽

Analytical Electron Microscopy ◽

Incident Beam ◽

Thin Foil ◽

Experimental Conditions ◽

X Ray ◽

Microchemical Analysis ◽

Analytical Electron ◽

Image Position ◽

Incident Beam Energy

The ultimate sensitivity of microchemical analysis using x-ray emission rests in selecting those experimental conditions which will maximize the measured peak-to-background (P/B) ratio. This paper presents the results of calculations aimed at determining the influence of incident beam energy, detector/specimen geometry and specimen composition on the P/B ratio for ideally thin samples (i.e., the effects of scattering and absorption are considered negligible). As such it is assumed that the complications resulting from system peaks, bremsstrahlung fluorescence, electron tails and specimen contamination have been eliminated and that one needs only to consider the physics of the generation/emission process.The number of characteristic x-ray photons (Ip) emitted from a thin foil of thickness dt into the solid angle dΩ is given by the well-known equation

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X-ray microanalysis of thin specimens in the transmission electron microscope at voltages up to 1000 Kv.

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109847 ◽

1978 ◽

Vol 36 (1) ◽

pp. 540-541

Author(s):

G. Cliff ◽

M.J. Nasir ◽

G.W. Lorimer ◽

N. Ridley

Keyword(s):

Electron Microscope ◽

Transmission Electron Microscope ◽

Weight Fraction ◽

Present Series ◽

Constant Independent ◽

X Ray ◽

Transmission Electron ◽

Series Of Experiments ◽

Image Position ◽

X Ray Absorption

In a specimen which is transmission thin to 100 kV electrons - a sample in which X-ray absorption is so insignificant that it can be neglected and where fluorescence effects can generally be ignored (1,2) - a ratio of characteristic X-ray intensities, I1/I2 can be converted into a weight fraction ratio, C1/C2, using the equationwhere k12 is, at a given voltage, a constant independent of composition or thickness, k12 values can be determined experimentally from thin standards (3) or calculated (4,6). Both experimental and calculated k12 values have been obtained for K(11<Z>19),kα(Z>19) and some Lα radiation (3,6) at 100 kV. The object of the present series of experiments was to experimentally determine k12 values at voltages between 200 and 1000 kV and to compare these with calculated values.The experiments were carried out on an AEI-EM7 HVEM fitted with an energy dispersive X-ray detector.

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