Image restoration through aberrant media by optical phase conjugation in a type II three-wave mixing interaction

Restoration of an image through an aberrant plate has been achieved by use of optical phase conjugation in a type II parametric interaction in which the amplified signal and idler waves are reflected back through the aberrant medium. The resolution of the restored phase-conjugate images is equal to 0.18 mm, and the amplification gain is ~4dB.     

Graphical thresholding procedure and optimal light level estimation for spatially resolved photon counting with EMCCDs

Thanks to the electron multiplying function that can effectively convert the weak incident photon signal to amplified electron output, electron multiplying charged-coupled devices (EMCCDs) are becoming useful and popular detectors in photon counting regimes necessitating also spatial resolution. A multi-imaging strategy has been already proposed and experimentally tested to improve the accuracy of photon counting with an EMCCD, by taking into account the random nature of its on-chip gain and the possibility of multiple photodetection events on 1 pixel. In this paper, referring to the thresholding procedure developed for photon counting, we present a clear graphical method for the threshold and the optimal light level estimations. Thanks to the graphical visualization of the probabilities involved in the detection errors on 1 pixel, we are able to derive in a straightforward way and for any EMCCD, the threshold level and thus the best mean level of illumination to be used in order to minimize the false detection probabilities that might ruin the image statistics, especially in cases where quantum spatial effects might be observed.     

Precise determination of the unperturbed 8B neutrino spectrum

A measurement of the final state distribution of the (8)B β decay, obtained by implanting a (8)B beam in a double-sided silicon strip detector, is reported here. The present spectrum is consistent with a recent independent precise measurement performed by our collaboration at the IGISOL facility, Jyv?skyl? [O. S. Kirsebom et al., Phys. Rev. C 83, 065802 (2011)]. It shows discrepancies with previously measured spectra, leading to differences in the derived neutrino spectrum. Thanks to a low detection threshold, the neutrino spectrum is for the first time directly extracted from the measured final state distribution, thus avoiding the uncertainties related to the extrapolation of R-matrix fits. Combined with the IGISOL data, this leads to an improvement of the overall errors and the extension of the neutrino spectrum at high energy. The new unperturbed neutrino spectrum represents a benchmark for future measurements of the solar neutrino flux as a function of energy.     

Numerical simulation of spatial fluctuations in parametric image amplification

We study the properties of the spatial fluctuations in the far-field parametric fluorescence output of a type 1 degenerate traveling-wave parametric amplifier. Results of a semi-classical simulation are compared with experiments in a LBO crystal. This simulation is then used to predict amplified images of a continuous background, in a phase-sensitive as well as in a phase-insensitive configuration. Received 12 March 2001     

Ein colorimetrisches Verfahren zur Auffindung kleiner Mengen Salpeters?ure wird

Ohne Zusammenfassung     

Factorization of monic polynomials

We prove a uniqueness result about the factorization of a monic polynomial over a general commutative ring into comaximal factors. We apply this result to address several questions raised by Steve McAdam. These questions, inspired by Hensel's Lemma, concern properties of prime ideals and the factoring of monic polynomials modulo prime ideals.

     

Experimental Study of Bacterial Penetration into Chalk Rock: Mechanisms and Effect on Permeability

Bacterial selective plugging is one of the mechanisms through which microorganisms can be applied for enhanced oil recovery, as bacteria can plug the water-swept zones of a reservoir, thus altering the flow paths and improving sweep efficiency. However, complete understanding of the penetration behavior of bacteria is lacking, especially in chalk formations where characteristic pore throat sizes are comparable with the sizes of bacterial cells. In this study, two bacterial strains, Bacillus licheniformis 421 (spore-forming) and Pseudomonas putida K12 (non-spore forming) were used to investigate the penetration of bacteria into chalk and its effect on permeability reduction. The core plugs were produced from Stevns Klint outcrop with low permeability (2–4 mD) and with pore sizes comparable to bacterial sizes. Both types of bacteria were able to penetrate and to be transported through the cores to some extent. A significantly higher number of B. licheniformis 421 was detected in the effluents as compared to P. putida K12. It was demonstrated that the spore-forming B. licheniformis 421 penetrates in the form of spores. P. putida K12 is found to penetrate the core, however, in smaller numbers compared to B. licheniformis. It was shown that both bacteria, under different injection concentrations, were capable of plugging the porous rock, as indicated by reduction of the core permeability. An incubation period of 12 days did not allow the permeability to return to initial condition. Based on the results it can be concluded that, when injected into chalk, spore forming bacteria have higher chance to survive and penetrate into deeper formation; and both types of bacteria may cause permeability reduction.     

Atomistic wear in a single asperity sliding contact

Abrasive wear of sharp silicon tips sliding distances of up to 750 m on a polymeric surface is studied using atomic force microscopy. The data cannot be explained by conventional macroscopic wear models. We present a new model in which the barrier for breaking an atomic bond is lowered by the frictional stress acting on the contact. Quantitative agreement is obtained between the model and wear data for all load forces and sliding distances studied.     

Two-dimensional time-resolved direct imaging through thick biological tissues: a new step toward noninvasive medical imaging

We report an original two-dimensional time-resolved direct imaging method for transillumination optical tomography that combines the time-gating and forward phase-conjugation properties of type II degenerate parametric amplification. An object with subcentimeter resolution embedded in 4-cm-thick chicken breast tissue was imaged with a signal-to-noise ratio of 2.