Opto-acoustic modulator with a nematic liquid crystal

A liquid-crystal optical modulator working with acoustic signals is considered. It is shown that it can be operated also with white light up to frequencies of at least 1 MHz.     

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Effect of nanoparticles on the interfacial properties of liquid/liquid and liquid/air surface layers

An investigation is reported on the interfacial properties of nanometric colloidal silica dispersions in the presence of a cationic surfactant. These properties are the result of different phenomena such as the particle attachment at the interface and the surfactant adsorption at the liquid and at the particle interfaces. Since the latter strongly influences the hydrophobicity/lipophilicity of the particle, i.e., the particle affinity for the fluid interfacial environment, all those phenomena are closely correlated. The equilibrium and dynamic interfacial tensions of the liquid/air and liquid/oil interfaces have been measured as a function of the surfactant and particle concentration. The interfacial rheology of the same systems has been also investigated by measuring the dilational viscoelasticity as a function of the area perturbation frequency. These results are then crossed with the values of the surfactant adsorption on the silica particles, indirectly estimated through experiments based on the centrifugation of the dispersions. In this way it has been possible to point out the mechanisms determining the observed kinetic and equilibrium features. In particular, an important role in the mixed particle-surfactant layer reorganization is played by the Brownian transport of particles from the bulk to the interface and by the surfactant redistribution between the particle and fluid interface.     

Limit Processes for TASEP with Shocks and Rarefaction Fans

We consider the totally asymmetric simple exclusion process (TASEP) with two-sided Bernoulli initial condition, i.e., with left density ρ ₋ and right density ρ ₊. We study the associated height function, whose discrete gradient is given by the particle occurrences. Macroscopically one has a deterministic limit shape with a shock or a rarefaction fan depending on the values of ρ _±. We characterize the large time scaling limit of the multipoint fluctuations as a function of the densities ρ _± and of the different macroscopic regions. Moreover, using a slow decorrelation phenomena, the results are extended from fixed time to the whole space-time, except along the some directions (the characteristic solutions of the related Burgers equation) where the problem is still open.     

Directional edge enhancement using a liquid-crystal display

We present a method for orientation-selective enhancement of the first derivatives of an image. The proposed method is based on the polarization properties of the twisted-nematic liquid-crystal displays (LCDs). LCDs are manufactured to work between a polarizer-analyzer pair, and for a given incident polarization direction, the image contrast will depend on the analyzer orientation. In particular, two analyzer orientations of interest could be identified for the proposed experiments: one that reproduces the image displayed on the LCD, and the other one (orthogonal to the former) that gives a negative (contrast reversed) replica of the original image. By placing a beamsplitter after the LCD, two images are spatially separated, analyzed by linear polarizers in perpendicular directions, and then slightly displaced. When the original image and its displaced (contrast reverted) replica are imagined together across a plane, one obtains a resultant image with enhanced first derivatives along a specific direction. Unlike the usual Fourier (coherent) image processing, the technique proposed here works with incoherent illumination. Validation experiments are presented.     

Pulse-width modulation in defocused three-dimensional fringe projection

Shape measurements by fringe projection methods require high-quality sinusoidal fringes. We present a sinusoidal fringe generation technique that utilizes slightly defocused binary fringe projection. The proposed method is a spatial version of the well-known pulse-width modulation (PWM) technique of electrical engineering. PWM is easy to implement using off-the-shelf projectors, and it allows us to overcome the gamma problem (i.e., the nonlinear projector response) in the output light intensity. We will demonstrate that, with a small defocusing level--lower than with other techniques proposed in the literature--a high-quality sinusoidal pattern is obtained. Validation experiments using a commercial video projector are presented.     

Limit process of stationary TASEP near the characteristic line

The totally asymmetric simple exclusion process (TASEP) on\input amssym ${\Bbb Z}$ with the Bernoulli‐ρ measure as an initial condition, 0 < ρ < 1, is stationary. It is known that along the characteristic line, the current fluctuates at an order of t^1/3. The limiting distribution has also been obtained explicitly. In this paper we determine the limiting multipoint distribution of the current fluctuations moving away from the characteristics by the order t^2/3. The main tool is the analysis of a related directed last percolation model. We also discuss the process limit in tandem queues in equilibrium. © 2010 Wiley Periodicals, Inc.     

Quasicrystalline electronic states of a one-dimensionally modulated Ag film

Ag films on GaAs(110) exhibit a one-dimensional quasiperiodic modulation, resulting in a Fibonacci sequence of parallel stripes with two different widths. Valence level photoemission shows that the Ag electronic states acquire a unique character along the quasiperiodic direction, distinctively manifested by a hierarchy of energy level replicas and avoided crossings at characteristic intervals in reciprocal space. These observations demonstrate the strong influence of the one-dimensional quasiperiodic potential on the Ag film states.