This paper describes the application of a laser diffraction technique to the study of electroconvection in nematic liquid crystal cells. It allows a real-time quantitative access to pattern wave lengths and amplitudes. The diffraction profile of the spatial periodic pattern is calculated and compared quantitatively to experimental intensity profiles. For small director tilt amplitudes ϕ, the phase grating generated in normally incident undeflected light and the first order term correction from light deflection is derived analytically. It yields an I ∝ ϕ 4 dependence of the diffracted intensity I on the amplitude of director deflections. For larger director tilt amplitudes, phase and amplitude modulations of deflection of light in the inhomogeneous director field are calculated numerically. We apply the calculations to the determination of the director deflection and measure growth and decay rates of the dissipative patterns under periodic excitation. Real time analysis of pattern amplitudes under stochastic excitation is demonstrated. PACS. 4 2.70.Df (Liquid Crystals), 47.20.-k (Hydrodynamic instability), 78.20.-e (Optical Properties of bulk materials and thin films).

Two-dimensional pendant liquid expanded droplets partially wet the liquid condensed/gas-phase boundaries in methyl octadecanoate Langmuir monolayers. Their shape is described by the Young−Laplace equation including long-range electrostatic interactions on a scale Δ. It is invariant under shape-invariant scale transformations. We show that the local stability at the three-phase intersection point is described by Young's equation for the contact angle. The contact angle is not invariant under shape-invariant scale transformations but is a materials constant at a fixed scale parameter Δ. By comparison of numerically simulated droplets with experimental droplets observed with a fluorescence microscope, we determine the spreading coefficient of wetting Langmuir monolayer phases as well as a lower limit for Δ. We find 0.12 μm < Δ and suggest that the scale parameter shall be interpreted as a dipolar correlation length, not as a molecular cutoff length.

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Typical metal detectors work at very low to low frequencies. In this paper, a metal/anomaly detector design that operates in the high to very high frequency range is presented. This design uses a high-Q tuned loop antenna for metal/anomaly detection. By measuring the return loss or voltage standing wave ratio a frequency notch can be detected. Tuning to the optimal location of the notch can be accomplished by monitoring the phase response. This phase monitoring technique can be used to ground balance the detector. As a metal object is moved along the longitudinal axis of the loop antenna a substantial shift in the frequency of the notch is detected. For metal targets, the frequency shift is positive, and for ferrite and other targets, the frequency shift is negative. This frequency shift is created by the proximity of the target causing a change in the impedance of the antenna. Experiments with a prototype antenna show long-range detection with low power requirements. The detector requires only one loop with one winding which is used for both transmit and receive. This allows for a metal/anomaly detector with a very simple design. The design is lightweight and, depending on loop size, significantly increases detection depth performance. In the full paper, modeling and further experimental results will be presented. Performance results for various types of soil and for different types of targets are presented.