Chemically controlled pattern formation in phase-separating materials

Summary The role of chemical reactions in the selection of patterns in phase-separating mixtures is presented. Linearized theory and computer simulation show that the initial long-wavelength instability characteristic of spinodal decomposition is suppressed by chemical reactions, which restrict domain growth to intermediate length scales even in the late stages of phase separation. Our findings suggest that chemical reactions may provide a novel way to stabilize and tune the steady-state morphology of phase-separating materials. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Are the proposed cosmic H particles psionlike in Nature?

Summary The hints to explain the unusual type of cosmic cluster events (called generally the ?exotic? events) in ultrahigh-energy nuclear collisions in terms of proposed H particles have, to date, been neither substantiated nor concretised. We assort here some crucial aspects and assemble a few supportive evidences to favour our idea that the proposed H particles might be viewed as cosmic psionlike particles.     

Optical waveguide analysis using modified Airy functions

We review a little-used but powerful method of solving the scalar wave equation. It uses a modification of the well-known Airy functions, which are easily calculated on desktop computers. The techniques are reminiscent of the WKBJ methodology, but the solution, although approximate, is much more useful than the traditional WKBJ solution and can be used with almost as much ease. Re method is extremely powerful but, to our knowledge, is not used in the optics community. It is useful in analyzing integrated optical waveguide components.     

Serial magnetic resonance imaging in patients following acute myocardial infarction.

The detection of serial changes in magnetic resonance (MR) signal intensity of the heart following acute myocardial infarction may provide a useful method of characterizing tissue healing. Fourteen patients with acute Q-wave infarction underwent T2-weighted, spin-echo cardiac imaging during hospitalization, followed by one or more additional MR studies (total 31) over a 6- to 27-wk period (mean: 3 mo). Visual assessment of the images demonstrated a gradual reduction in signal intensity and localization of the bright signal to the subendocardium of the infarction region over the three-mo study period. A quantitative measurement of signal intensity (infarction/normal myocardium) fell from 1.81 +/- 0.42 on the initial study to 1.34 +/- 0.37 (p less than 0.05) at a mean of 14 wk. Two patients had an increase in signal intensity on the follow-up study and both patients had been readmitted with acute coronary syndromes. In summary, characterization of changes in signal intensity may provide a useful method of assessing myocardial healing following acute myocardial infarction. Further studies are indicated to determine the prognostic significance of these parameters.     

The 3-D FEL pulse propagation equation: An analytical treatment in the low-gain and small-signal regime

Summary In this paper we show that the transverse mode evolution of a FEL operating with short pulses can be treated, in the small-signal and low-gain regime, using a relatively simple mathematical technique leading to a potentially fast numerical algorithm. We also point out that analytical solutions can be obtained for the cases where the slippage length is small compared to the longitudinal bunch length.     

Characterization of carbide phases in high speed tool steels

A study is reported on carbides electrolytically extracted from two different types of high speed tool steels as quenched and after tempering. According to X-ray diffraction analysis and EDS microanalysis, Mössbauer spectra show the presence of MC and M₆C in every analysed sample. Only a few substitutional Fe atoms should be present in MC and they give a minor contribution to the Mössbauer spectrum. A model for evaluating the Mössbauer spectrum of M₆C is proposed which is based on the symmetry of lattice sites occupied by Fe atoms and partially substituted by other metallic atoms. The proposed model also allows to get information on the amount of this substitution.     

Search for cosmic γ-ray bursts in the (1÷50) GeV energy range

Summary A search for cosmic gamma-ray bursts in the GeV energy range has been performed by means of the EAS-TOP Extensive Air Shower array at Campo Imperatore (Gran Sasso Laboratories) during the period March–December 1990. In 2566.5 hours of measurement the obtained upper limit to the rate of bursts of amplitude >2% of the cosmic-ray intensity and time duration τ=1 s, isR≤7.9y⁻¹ (90% c.l.). Assuming for γ-rays a differential energy spectrumS(E ₀ )≈E ₀ ^−2.5 , the corresponding upper limit to the energy flux of γ-rays with energy >5 GeV in bursts of duration τ≤1 s is Φ<8.3·10⁻⁵erg cm⁻².     

The electron current to a Langmuir probe in a flowing high-pressureplasma

The electron current to a Langmuir probe in a moving high-pressure plasma has been measured and analyzed. The plasma is an atmospheric-pressure propane flame, and the probe's speed relative to the plasma was varied from 10 ms^-1 to 30 ms^-1. The current is linearly dependent on the speed and appears to be comprised of two components-one driven by diffusion and the other by convection. A model is devised which can be used to measure the electron density. By comparing the density computed from this model to that measured from the ion current, it has been possible to measure the electron mobility in the flame gases. The value obtained by the authors is in good agreement with theoretical calculations found in the literature