Mars riometer system

A riometer (relative ionospheric opacity meter) measures the intensity of cosmic radio noise at the surface of a planet. When an electromagnetic wave passes through the ionosphere collisions between charged particles (usually electrons) and neutral gases remove energy from the wave. By measuring the received signal intensity at the planet's surface and comparing it to the expected value (the quietday curve) a riometer can deduce the absorption (attenuation) of the trans-ionospheric signal. Thus the absorption measurements provide an indication of ionisation changes occurring in the ionosphere. To avoid the need for orbiting sounders riometers use the cosmic noise background as a signal source. Earth-based systems are not subject to the challenging power, volume and mass restriction that would apply to a riometer for Mars. Some Earth-based riometers utilise phased-array antennas in order to provide an imaging capability.UnpublishedVienna - Austria3.9. Fisica della magnetosfera, ionosfera e meteorologia spazialeope

Physics of Auroral Phenomena

Abstract. Observations of aurora by highly sensitive television (TV) cameras and of riometric absorption by IRIS imaging riometer allows one to study spatialtemporal dynamics of precipitated particles

Robustly estimating the flow direction of information in complex physical systems

We propose a new measure to estimate the direction of information flux in multivariate time series from complex systems. This measure, based on the slope of the phase spectrum (Phase Slope Index) has invariance properties that are important for applications in real physical or biological systems: (a) it is strictly insensitive to mixtures of arbitrary independent sources, (b) it gives meaningful results even if the phase spectrum is not linear, and (c) it properly weights contributions from different frequencies. Simulations of a class of coupled multivariate random data show that for truly unidirectional information flow without additional noise contamination our measure detects the correct direction as good as the standard Granger causality. For random mixtures of independent sources Granger Causality erroneously yields highly significant results whereas our measure correctly becomes non-significant. An application of our novel method to EEG data (88 subjects in eyes-closed condition) reveals a strikingly clear front-to-back information flow in the vast majority of subjects and thus contributes to a better understanding of information processing in the brain.Comment: 5 pages, 4 figure

GIS-Based Estimation of Exposure to Particulate Matter and NO(2) in an Urban Area: Stochastic versus Dispersion Modeling

Stochastic modeling was used to predict nitrogen dioxide and fine particles [particles collected with an upper 50% cut point of 2.5 μm aerodynamic diameter (PM(2.5))] levels at 1,669 addresses of the participants of two ongoing birth cohort studies conducted in Munich, Germany. Alternatively, the Gaussian multisource dispersion model IMMIS(net/em) was used to estimate the annual mean values for NO(2) and total suspended particles (TSP) for the 40 measurement sites and for all study subjects. The aim of this study was to compare the measured NO(2) and PM(2.5) levels with the levels predicted by the two modeling approaches (for the 40 measurement sites) and to compare the results of the stochastic and dispersion modeling for all study infants (1,669 sites). NO(2) and PM(2.5) concentrations obtained by the stochastic models were in the same range as the measured concentrations, whereas the NO(2) and TSP levels estimated by dispersion modeling were higher than the measured values. However, the correlation between stochastic- and dispersion-modeled concentrations was strong for both pollutants: At the 40 measurement sites, for NO(2), r = 0.83, and for PM, r = 0.79; at the 1,669 cohort sites, for NO(2), r = 0.83 and for PM, r = 0.79. Both models yield similar results regarding exposure estimate of the study cohort to traffic-related air pollution, when classified into tertiles; that is, 70% of the study subjects were classified into the same category. In conclusion, despite different assumptions and procedures used for the stochastic and dispersion modeling, both models yield similar results regarding exposure estimation of the study cohort to traffic-related air pollutants

New approaches to coding information using inverse scattering transform

Remarkable mathematical properties of the integrable nonlinear Schrödinger equation (NLSE) can offer advanced solutions for the mitigation of nonlinear signal distortions in optical fiber links. Fundamental optical soliton, continuous, and discrete eigenvalues of the nonlinear spectrum have already been considered for the transmission of information in fiber-optic channels. Here, we propose to apply signal modulation to the kernel of the Gelfand-Levitan-Marchenko equations that offers the advantage of a relatively simple decoder design. First, we describe an approach based on exploiting the general N-soliton solution of the NLSE for simultaneous coding of N symbols involving 4×N coding parameters. As a specific elegant subclass of the general schemes, we introduce a soliton orthogonal frequency division multiplexing (SOFDM) method. This method is based on the choice of identical imaginary parts of the N-soliton solution eigenvalues, corresponding to equidistant soliton frequencies, making it similar to the conventional OFDM scheme, thus, allowing for the use of the efficient fast Fourier transform algorithm to recover the data. Then, we demonstrate how to use this new approach to control signal parameters in the case of the continuous spectrum

Minimizing Variability of Cascade Impaction Measurements in Inhalers and Nebulizers

The purpose of this article is to catalogue in a systematic way the available information about factors that may influence the outcome and variability of cascade impactor (CI) measurements of pharmaceutical aerosols for inhalation, such as those obtained from metered dose inhalers (MDIs), dry powder inhalers (DPIs) or products for nebulization; and to suggest ways to minimize the influence of such factors. To accomplish this task, the authors constructed a cause-and-effect Ishikawa diagram for a CI measurement and considered the influence of each root cause based on industry experience and thorough literature review. The results illustrate the intricate network of underlying causes of CI variability, with the potential for several multi-way statistical interactions. It was also found that significantly more quantitative information exists about impactor-related causes than about operator-derived influences, the contribution of drug assay methodology and product-related causes, suggesting a need for further research in those areas. The understanding and awareness of all these factors should aid in the development of optimized CI methods and appropriate quality control measures for aerodynamic particle size distribution (APSD) of pharmaceutical aerosols, in line with the current regulatory initiatives involving quality-by-design (QbD)

Cherenkov radiation emitted by ultrafast laser pulses and the generation of coherent polaritons

We report on the generation of coherent phonon polaritons in ZnTe, GaP and LiTaO$_{3}$ using ultrafast optical pulses. These polaritons are coupled modes consisting of mostly far-infrared radiation and a small phonon component, which are excited through nonlinear optical processes involving the Raman and the second-order susceptibilities (difference frequency generation). We probe their associated hybrid vibrational-electric field, in the THz range, by electro-optic sampling methods. The measured field patterns agree very well with calculations for the field due to a distribution of dipoles that follows the shape and moves with the group velocity of the optical pulses. For a tightly focused pulse, the pattern is identical to that of classical Cherenkov radiation by a moving dipole. Results for other shapes and, in particular, for the planar and transient-grating geometries, are accounted for by a convolution of the Cherenkov field due to a point dipole with the function describing the slowly-varying intensity of the pulse. Hence, polariton fields resulting from pulses of arbitrary shape can be described quantitatively in terms of expressions for the Cherenkov radiation emitted by an extended source. Using the Cherenkov approach, we recover the phase-matching conditions that lead to the selection of specific polariton wavevectors in the planar and transient grating geometry as well as the Cherenkov angle itself. The formalism can be easily extended to media exhibiting dispersion in the THz range. Calculations and experimental data for point-like and planar sources reveal significant differences between the so-called superluminal and subluminal cases where the group velocity of the optical pulses is, respectively, above and below the highest phase velocity in the infrared.Comment: 13 pages, 11 figure

Evaluation of laser-glazed plasma-sprayed thermal barriercoatings under high temperature exposure to molten salts

Thermal Barrier Coating (TBC) systems are frequently used in gas turbine engines to provide thermal insulation to the hot-section metallic components and also to protect them from oxidation, hot corrosion and erosion. Surface sealing treatments, namely laser-glazing, have been showing a high potential for extending in-service lifetimes of these systems by improving chemical and thermo-mechanical resistance. In this investigation, both as-sprayed and laser-glazed TBCs were exposed to hot corrosion in molten salts. The glazed coatings were obtained by scanning the surface of the plasma-sprayed coatings with either a CO2 or a Nd:YAG laser. The hot corrosion investigation was accomplished by subjecting the specimens to an isothermal air furnace testing under V2O5 and/or Na2SO4 at a temperature of 1000 °C for 100 h. Spallation has been observed in coatings in the as-sprayed condition under V2O5 or V2O5+Na2SO4. Na2SO4 itself had no or minimal effect on the degradation of the laser-glazed or as-sprayed condition coatings, respectively. The degradation in V2O5 was accomplished by destabilization of YSZ as a consequence of depletion of yttria from the solid solution to form YVO4 and therefore led to the disruptive transformation of the metastable tetragonal phase to the monoclinic phase. Moreover, the presence of both corrosive salts induced the formation of large high aspect ratio YVO4 crystals that introduced additional stresses and contributed to the degradation of the coatings. The laser-glazed specimens were not efficient in avoiding the molten salt penetration along the thickness direction due to the presence of cracks on the glazed layer. However due to a reduced specific surface area of the dense glazed layer, the corrosion reaction of the molten salts with the YSZ has been lower than in coatings in the assprayed condition.Fundo Europeu de Desenvolvimento Regional(FEDER) - Programa Operacional "Ciência, Tecnologia e Inovação" (POCTI).Fundação para a Ciência e a Tecnologia (FCT) - Project POCTI/CTM/ 44590/2002

Poboljšana elektromagnetska kompatibilnost (EMC) sklopnog energetskog pretvarača sa slučajnom modulacijom

This paper surveys some analytical and experimental results concerning different randomized modulation strategies in switched-mode power converters (SMPCs). After a short review of practical experiences within the literature it presents the benefits of several randomized schemes for power converters (i.e. reduced electromagnetic interference - EMI, and lower acoustic noise). It also introduces the mathematical background for dealing with randomized modulation within the medium-frequency range: power spectrum density (PSD). Finally, the EMI measurements confirm the improved EMC performances of the randomized boost rectifier, as also in the DC-DC buck converter.Ovaj članak istražuje analitičke i eksperimentalne rezultate različitih slučajnih strategija modulacije u sklopnim energetskim pretvaračima (SMPCs). Nakon kratkog pregleda praktičnih iskustava iz literature, predstavljene su prednosti nekoliko slučajnih shema za energetske pretvarače (smanjena elektromagnetska interferencija - EMI, i niži akustični šum). Također, uvedena je matematička podloga za rad sa slučajnom modulacijom u području srednjih frekvencija: spektralna gustoća snage (PSD). Konačno, EMI mjerenja potvrđuju poboljšanja EMC performansi slučajnih uzlaznih ispravljača, kao i DC-DC silaznih pretvarača