Learning Markov chains in fractal compression of image data

In a recent paper [17] we proposed a stochastic algorithm which generates optimal probabilities for the decompression of an image represented by the fixed point of an IFS system (SAOP). We show here that such an algorithm is in fact a non trivial example of Generalized Random System with Complete Connections. We also exhibit a generalization which could represent the solution to the inverse problem for an image with grey levels, if a fixed set of contraction maps is available. Received: 1 July 2002     

Interaction of polar molecules with resonant radio frequency electric fields: imaging of the NO molecular beam splitting

The interaction between a NO supersonic beam and a resonant radio frequency (RF) field is investigated using laser ionization coupled to imaging techniques. It is shown how the resonant interaction leads to a beam splitting of +/-0.2 degrees toward both positive and negative direction perpendicular to the beam propagation axis. This phenomenon is rationalized using a model based on molecular interferences produced by the action of the resonant RF electric field.     

CRTA Study of the Reduction of UO2F2 into UO2 by Dry H2

The reduction of UO₂F₂ by dry H₂ was studied by Controlled Rate EGA, with a special set-up operating under a gas flow under atmospheric pressure. At the constant transformation rate selected, this reduction apparently takes place in one main step, around 450°C (for a total duration of 100 h), followed by a small exothermic step. The final product is a stoichiometric, well crystallized UO₂. XRD analysis shows the occurrence of two successive intermediates of which one has a structure close to that of UO₂, but with interstitial fluorine atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecular beam electric resonance without A- and B-fields

We report on a novel phenomenon observed during the passage of a pulsed NO beam seeded in He through a combined homogeneous, static electric and RF field, denoted as C-field in a standard molecular beam electric resonance (MBER) experiment. Although we refrain from the state selective A- and B-fields, which are considered crucial for a MBER experiment, the transmitted intensity exhibits as a function of the RF frequency conspicuous dips at resonance frequencies that depend strictly linearly on the static field strength E ₀. Their spectral width is by a factor of 4 smaller than the time of flight broadening. Both, the resonance frequencies and their linear field dependence can be precisely predicted applying a simple expression for the Stark effect to a transition of a single rotational state (J = 3/2) of the electronic ground state . However, this formula is valid only in the high field limit (E ₀ > 1000 kV/m) while the employed field (E ₀ = 1.47 kV/m) was in the extreme low field domain where the large type doubling and hyperfine coupling lead to a purely quadratic Stark effect. We assume that the phenomenon is due to a yet unknown collective rather than to an isolated particle process.Received: 9 May 2003, Published online: 12 August 2003PACS: 33.20.Bx Radio-frequency and microwave spectra - 32.60. + i Zeeman and Stark effects Author for correspondence: A. González Ureña     

Photochemistry and reactions of OH− defects and F centers in Alkali Halides

Additively colored KCl:OH^? crystals show under combined UV and visible irradiation an irreversible destruction of F centers and visible absorption. This process, which is effective over the whole temperature range 4–300 K, was studied systematically in terms of the reaction efficiency and products using UV-visible and IR (local mode) spectroscopy. The UV photo-dissociation of OH^? defects and photo-ionization of F centers produce a combined net effect, in which at higher temperatures all F centers are converted into U centers, thus completely bleaching the colored crystal. By these photo-reactions, high contrast visible images can be produced which are stable under visible light at RT, and are thermally stable up to 650°C. Besides the optical information-storage aspect, these photo-reactions can be used for controlled production of U_A centers if the crystal contains alkali-ion impurities like Na⁺.     

Self supported nickel antimonides based electrodes for Li ion battery

Self-supported nickel antimonides/Ni architectured electrodes were prepared by solid state reaction from Ni thin film, Ni foam and Ni nanorods. This specific design is expected to optimize both NiSb_x/Ni-current collector and NiSb_x/electrolyte interfaces of the electrode in the Li ion battery. This new electrode preparation process is based on solid state reaction of antimony with the nickel architectured substrate. Preliminary electrochemical tests of the as-obtained self supported antimonide electrodes show improvement in the capacity retention of the NiSb_x active material.     

Enzyme Conformation Influences the Performance of Lipase-powered Nanomotors

Enzyme-powered micro/nanomotors have myriads of potential applications in various areas. To efficiently reach those applications, it is necessary and critical to understand the fundamental aspects affecting the motion dynamics. Herein, we explored the impact of enzyme orientation on the performance of lipase-powered nanomotors by tuning the lipase immobilization strategies. The influence of the lipase orientation and lid conformation on substrate binding and catalysis was analyzed using molecular dynamics simulations. Besides, the motion performance indicates that the hydrophobic binding (via OTES) represents the best orienting strategy, providing 48.4 % and 95.4 % increase in diffusion coefficient compared to hydrophilic binding (via APTES) and Brownian motion (no fuel), respectively (with C_[triacetin] of 100 mm ). This work provides vital evidence for the importance of immobilization strategy and corresponding enzyme orientation for the catalytic activity and in turn, the motion performance of nanomotors, and is thus helpful to future applications.     

Color center production by femtosecond-pulse laser irradiation in fluoride crystals

Color centers are lattice vacancy defects trapping electrons or holes. They are easily created in single crystals by irradiation with ionizing radiation. We report the production of color centers in LiF and LiYF₄ single crystals by ultrashort high-intensity laser pulses (60 fs, 12.5 GW). An intensity threshold for color center creation of 1.9 and 2 TW/cm² was determined in YLF and LiF, respectively, which is slightly smaller than the continuum generation threshold. Due to the high energy density of the coherent radiation of the focused laser beam, we were able to identify a large amount of F centers, which gave rise to aggregates such as F₂, F ₂ ⁺ , and F ₃ ⁺ . The proposed mechanism of formation is based on multiphoton excitation, which also produces short-lived F ₂ ⁺ centers. It is also shown that it is possible to write tracks in the LiF crystals with dimensional control.     

Glass surface as strong base, ‘green’ heterogeneous catalyst and degradation reagent

Systematic screening of accelerated chemical reactions at solid/solution interfaces has been carried out in high-throughput fashion using desorption electrospray ionization mass spectrometry and it provides evidence that glass surfaces accelerate various base-catalyzed chemical reactions. The reaction types include elimination, solvolysis, condensation and oxidation, whether or not the substrates are pre-charged. In a detailed mechanistic study, we provide evidence using nanoESI showing that glass surfaces can act as strong bases and convert protic solvents into their conjugate bases which then act as bases/nucleophiles when participating in chemical reactions. In aprotic solvents such as acetonitrile, glass surfaces act as ‘green’ heterogeneous catalysts that can be recovered and reused after simple rinsing. Besides their use in organic reaction catalysis, glass surfaces are also found to act as degradation reagents for phospholipids with increasing extents of degradation occurring at low concentrations. This finding suggests that the storage of base/nucleophile-labile compounds or lipids in glass containers should be avoided.

Glass surfaces are found to be strong bases, ‘green’ heterogeneous catalysts and degradation reagents: glass microspheres act as strong bases to accelerate multiple base-catalyzed reaction types by a factor of 26–2021.     

Stochastic Description of a Bose�CEinstein Condensate

In this work we give a positive answer to the following question: does Stochastic Mechanics uniquely define a three-dimensional stochastic process which describes the motion of a particle in a Bose?CEinstein condensate? To this extent we study a system of N trapped bosons with pair interaction at zero temperature under the Gross?CPitaevskii scaling, which allows to give a theoretical proof of Bose?CEinstein condensation for interacting trapped gases in the limit of N going to infinity. We show that under the assumption of strictly positivity and continuous differentiability of the many-body ground state wave function it is possible to rigorously define a one-particle stochastic process, unique in law, which describes the motion of a single particle in the gas and we show that, in the scaling limit, the one-particle process continuously remains outside a time dependent random ??interaction-set?? with probability one. Moreover, we prove that its stopped version converges, in a relative entropy sense, toward a Markov diffusion whose drift is uniquely determined by the order parameter, that is the wave function of the condensate.