Phase modulation of the signal beam in three-wave forward mixing in photorefractive bismuth silicon oxide

The interaction of three forward beams in a BSO crystal is investigated under conditions when the two pump beams are anti-symmetrically detuned and the signal beam is phase modulated. For sinusoidal phase modulation the signal gain is shown to be dependent on the instantaneous frequency detuning. Single and double maxima in gain are obtained depending on the voltage amplitude applied to the piezoelectric mirror. For triangular phase modulation a slight asymmetry is found in the gain versus detuning curve.     

A model for a uniform steady-state vacuum arc with a hot anode

A model is formulated and evaluated for a Uniform electrical discharge sustained in vapor evaporated from an arc-heated anode. The plasma potential is positive with respect to both the cathode and anode. For a Cu anode, the anodic vapor dominates the plasma for current densities exceeding 8 kA/m². The anode heating potential is approximately 6.5 V, and the dominant cooling mechanism is evaporation for current densities exceeding 20 kA/m². Over the range 10 to 10000 kA/m², the electron density increases from 8×10¹⁷ to 5×10²³ m^-3, while the ionization fraction rises from 0.3% to 4%. At the lower end of this current range the electrical resistivity of 4 mΩ-m is determined primarily by electron-neutral collisions, while with increasing current the resistivity decreases to 0.7 mΩ-m, with electron-ion collisions contributing an equal share. This hot-anode vacuum arc may have potential for industrial application as a macroparticle-free high-deposition-rate coating source     

Sequential nonlinear estimation with nonaugmented priors

How can the basic compatibility of theory and observations be investigated for nonlinear processes without requiring stochastic characterizations for residual error terms? The present paper proposes a flexible least-cost approach. For each possible estimatex for the sequence of process states, letc _D (x) andx _M(x) denote the costs incurred for deviations away from the prior dynamic specifications and prior measurement specifications, respectively. Define the cost-efficiency frontier to be the greatest lower bound for the set of all possible cost pairs [c _D (x),c _M(x)], conditional on the given observations. State sequence estimatesx that attain the cost-efficiency frontier indicate the possible ways that the actual process could have developed over time in a manner minimally incompatible with the prior dynamic and measurement specifications. An algorithm is developed for the exact sequential updating of the cost-efficient state sequence estimates as the duration of the process increases and additional observations are obtained.     

High pressure mössbauer studies of magnetic actinide systems

Due to the wider radial extent of 5f electrons when compared to their 4f counterparts, intermetallics of the light actinides show a broad spectrum of magnetic properties ranging from the localized magnetism of the lanthanides to the itinerant magnetism often found in transition metal compounds. One parameter which strongly influences the magnetic character of the compound is the actinide-actinide separation which can experimentally be varied by the application of high pressure. The question of 5f electron delocalization will be reviewed with respect to Moesshauer high pressure data on NpCo₂si₂, NpAl₂, NpOs₂ and new results will be presented of NpAs. The connection of hyperfine parameters with results of X-ray diffraction studies will be discussed.Work supported by the Bundesministerium für Forschung und Technologie, Federal Republic of Germany     

The high-T c superconductor Sr0.2Lai1.8CuO4: A direct and inverse-photoemission study

We have measured ultraviolet and inverse-photoemission spectra of the novel superconductor Sr₀₂La_1.8CuO₄. Our results compare favorably with recent band-structure calculations for La₂CuO₄.A full account of this work will be published elsewhere [1]     

Adhesion studies of latex film surfaces on the meso- and nanoscale

In this paper the effects of surface roughness and annealing temperature (T) of latex coating films on adhesion are discussed for the different stages of the film formation process. The surface free energy of latex films was assessed in terms of practical work of adhesion (W) (or adherence) using a custom-built adhesion-testing device (ATD), atomic force microscopy (AFM), and contact angle measurements. For preannealed latex films surface roughness averages (R_a) were determined from AFM height images and were related to the values of W obtained from ATD measurements at room temperature. The results obtained using these tests exhibiting surface behavior on different length scales indicate a dependence of the measured adhesion on surface roughness and temperature, as well as on the length scale of the measurements.First preannealed samples were studied, which were obtained by heat treatment above the respective glass transition temperatures (T_g). Increasing the temperature of preannealing resulted in a decrease of the adherence observed in ATD experiments at room temperature. However, on the nanoscale, using AFM, no significant variation of the adherence was observed. This observation can be explained by roughness arguments. Preannealing decreases roughness which results in lower adherence values measured by ATD while for essentially single asperity AFM experiments roughness has an insignificant effect. Specimens were also annealed over a constant period of time (90 min) at different temperatures. At the end of the heat treatment, adhesion was measured at the treatment temperature by ATD. The amplified effect of temperature observed in this case on adherence is attributed to the combination of roughness decrease and increasing test temperature. In a third set of experiments completely annealed samples were studied by ATD as well as by AFM as a function of temperature. With increasing T values ATD showed a decrease in adherence, which is attributed to a decreasing surface free energy of the annealed films at elevated T values. AFM, on the other hand, showed an opposite trend which is assigned to increasing penetration of the tip into the tip/wetting polymer samples versus increasing temperature. Finally, annealing isotherms as a function of time were investigated by ATD in situ at different temperatures. This last set of experiments allowed us to optimize annealing time and temperature to achieve complete curing.     

Decay Rates in Probability Metrics Towards Homogeneous Cooling States for the Inelastic Maxwell Model

We quantify the long-time behavior of solutions to the nonlinear Boltzmann equation for spatially uniform freely cooling inelastic Maxwell molecules by means of the contraction property of a suitable metric in the set of probability measures. Existence, uniqueness, and precise estimates of overpopulated high energy tails of the self-similar profile proved in ref. 9 are revisited and derived from this new Liapunov functional. For general initial conditions the solutions of the Boltzmann equation are then proved to converge with computable rate as t → ∞ to the self-similar solution in this distance, which metrizes the weak convergence of measures. Moreover, we can relate this Fourier distance to the Euclidean Wasserstein distance or Tanaka functional proving also its exponential convergence towards the homogeneous cooling states. The findings are relevant in the understanding of the conjecture formulated by Ernst and Brito in refs. 15, 16, and complement and improve recent studies on the same problem of Bobylev and Cercignani⁽⁹⁾ and Bobylev, Cercignani and one of the authors.⁽¹¹⁾     

Detection of silent temporal gaps in sinusoidal markers

Gap detection thresholds were measured by forced-choice procedure for conditions where the duration of a silent gap was varied adaptively between pairs of sinusoidal markers of the same or different frequency. Frequencies of the first sinusoid in a pair of markers ranged from F1 = 500 to 4000 Hz. Second-sinusoid marker frequencies F2 included F1 = F2, and usually frequencies 2%, 5%, 24%, and 50% higher than F1. In preliminary studies the role of presentation level (E/N0) on gap detection was considered. Preliminary data revealed confounding extraneous factors arising from gating transients and from overall stimulus (i.e., markers + gap) and/or masker duration cues. In the main experiments, the contributions of these extraneous cues were evaluated with experimental designs aimed at identifying and minimizing the confounding roles of these cues in gap detection. For conditions where extraneous gating transient cues were minimized (by presenting the sinusoidal markers in a continuous noise masker with random onset phase for the second sinusoid in every pair of markers) and overall stimulus duration cues were diminished (by randomizing the duration of each marker independently), gap detection thresholds increased from 5 to 90 ms as the frequency separation between F1 and F2 was increased by half an octave. When the gap detection thresholds were treated as filter attenuation values by normalizing and converting the data into decibels, the data were closely fit by the roex filter model. On average, the listeners' performances were modeled well by a constant-percentage (7%) bandwidth filter centered on F1.