Influence of the Feedback Filter on the Response of the Pulsed Digital Oscillator

This paper introduces a new feedback topology for the Pulsed Digital Oscillator (PDO) and compares it to the classical topology. The `classic' or single feedback topology, introduced in previous works, shows a strong behavior dependence on the damping losses in the MEMS resonator. A new double feedback topology is introduced here in order to help solving this problem. Comparative discrete-time simulations and preliminary experimental measurements have been carried out for both topologies, showing how the new double feedback topology may increase PDO performance for some frequency ranges.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Fossil group origins: VIII RXJ075243.6+455653 a transitionary fossil group

It is thought that fossil systems are relics of structure formation in the primitive Universe. They are galaxy aggregations that have assembled their mass at high redshift with few or no subsequent accretion. Observationally these systems are selected by large magnitude gaps between their 1st and 2nd ranked galaxies. Nevertheless, there is still debate over whether or not this observational criterium selects dynamically evolved ancient systems. We have studied the properties of the nearby fossil group RXJ075243.6+455653 in order to understand the mass assembly of this system. Deep spectroscopic observations allow us to construct the galaxy luminosity function (LF) of RXJ075243.6+455653 down to M*+ 6. The analysis of the faint-end of the LF in groups and clusters provides valuable information about the mass assembly of the system. In addition, we have analyzed the nearby large-scale structure around this group. We identified 26 group members within r200=0.9 Mpc. The LF of the group shows a flat faint-end slope ( -1.08 +/- 0.33). This low density of dwarf galaxies is confirmed by the low value of the dwarf-to-giant ratio (DGR = 0.99 +/- 0.49) for this system. Both the lack of dwarf galaxies and the low luminosity of the BGG suggests that RXJ075243.6+455653 still has to accrete mass from its nearby environment. This mass accretion will be achieved because it is the dominant structure of a rich environment formed by several groups of galaxies (15) within 7 Mpc from the group center and with +/- 1000$ km/s. RXJ075243.6+455653 is a group of galaxies that has not yet completed the process of its mass assembly. This new mass accretion will change the fossil state of the group. This group is an example of a galaxy aggregation selected by a large magnitude gap but still in the process of the accretion of its mass (Abridged).Comment: 9 pages, 9 figures, accepted in A&

Thermal X-ray emission from shocked ejecta in Type Ia Supernova Remnants. Prospects for explosion mechanism identification

The explosion mechanism behind Type Ia supernovae is a matter of continuing debate. The diverse attempts to identify or at least constrain the physical processes involved in the explosion have been only partially successful so far. In this paper we propose to use the thermal X-ray emission from young supernova remnants originated in Type Ia events to extract relevant information concerning the explosions themselves. We have produced a grid of thermonuclear supernova models representative of the paradigms currently under debate: pure deflagrations, delayed detonations, pulsating delayed detonations and sub-Chandrasekhar explosions, using their density and chemical composition profiles to simulate the interaction with the surrounding ambient medium and the ensuing plasma heating, non-equilibrium ionization and thermal X-ray emission of the ejecta. Key observational parameters such as electron temperatures, emission measures and ionization time scales are presented and discussed. We find that not only is it possible to identify the explosion mechanism from the spectra of young Type Ia Supernova Remnants, it is in fact necessary to take the detailed ejecta structure into account if such spectra are to be modeled in a self-consistent way. Neither element line flux ratios nor element emission measures are good estimates of the true ratios of ejected masses, with differences of as much as two or three orders of magnitude for a given model. Comparison with observations of the Tycho SNR suggests a delayed detonation as the most probable explosion mechanism. Line strengths, line ratios, and the centroid of the Fe Kalpha line are reasonably well reproduced by a model of this kind.Comment: 11 pages, 8 figures (5 of them color), accepted for publication by the Ap

Modelación del efecto de escenarios de cobertura sobre la migración de nutrientes (N, P2O5) en la cuenca alta del río Magdalena (Huila, Colombia)*

The combination of deforestation due to agricultural frontier expansion and the increased use of fertilizers due to agricultural intensification has lead to an increase in the load of sediments and pollutants that negatively affect water quality in rural areas. This problem is particularly serious in the Colombian Andean region. This study applies a hydrological simulation model to compare the effect of four vegetable coverage management scenarios on nutrient migration from agricultural practices in the Upper Magdalena river basin. The simulation of water movement over hillsides and channels, which was run using the MIKE SHE and MIKE 11 models, showed an acceptable performance (S/σ =0.84, R=0.82, R2=0.67). However, pollutant migration showed a very low sensitivity to vegetable coverage in the configuration of the different model simulations (p > 0.05), with reductions in pollutant loads ranging only between 2 and 4%. Such reductions have to do with the intrinsic properties of vegetation (which act like a barrier to sediment flow,) with its ability to increase soil infiltration (therefore reducing runoff,) and with nutrient absorption by plants

Epitaxial nanocrystalline tin dioxide thin films grown on (0001) sapphire by femtosecond pulsed laser deposition

Nanocrystalline tin dioxide (SnO2)(SnO2) thin films of different thicknesses were fabricated on the (0001) surface of α-Al2O3α-Al2O3 (sapphire) using femtosecond pulsed laser deposition. X-ray diffraction and transmission electron microscopy (TEM) analysis revealed that the microstructure of the films strongly depends on the film thickness. The films with a small thickness (<30 nm) are composed of nanosized columnar (100) oriented grains (3–5 nm in diameter) which grow epitaxially on the substrate with three different in-plane grain orientations. The (101) oriented grains (25 nm in diameter) appear when the film thickness becomes larger than a critical value (about 60 nm). The volume fraction of the (101) grains increases with film thickness. Cross-section TEM studies indicated that the (101) oriented grains nucleate on the top of the (100) oriented nanosized grains and show abnormal grain growth driven by surface energy minimization. As a result, the electrical transport properties are strongly dependent on the film thickness. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70608/2/APPLAB-79-5-614-1.pd

Effect of crystal defects on the electrical properties in epitaxial tin dioxide thin films

Epitaxial (101) tin dioxide thin films with thickness ranging from 6 and 100 nm were deposited on the (102) α-Al2O3(101̄2)α-Al2O3 substrate by femtosecond pulsed laser ablation. Due to the lattice and thermal expansion mismatch with the substrate, the SnO2SnO2 film shows interfacial misfit dislocations, antiphase boundaries (APBs), and partial dislocations. The APBs lie along the (01)(1̄01) planes with a displacement of 1/2[101]. The densities of APBs and partial dislocations vary with film thickness, whereas the average spacing of misfit dislocations remains constant. Hall effect measurements showed that both electron concentration and mobility decrease with a reduction in the film thickness, which is ascribed to the scattering of electrons by crystal defects and interfaces and the effect of a native space charge region at the near-surface region of the films. The response of the films to reducing gases was found to depend on the electron concentration of the film and the relative fraction, with respect to film thickness, of material that is depleted of electrons. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70824/2/APPLAB-81-27-5168-1.pd