Fast magnetosonic wave excitation by an array of wires with time-modulated currents

The excitation of Fast Magnetosonic (FMS)waves by a cylindrical array of parallel tethers carrying timemodulated current is discussed. The tethers would fly vertical in the equatorial plane, which is perpendicular to the geomagnetic field when its tilt is ignored, and would be stabilized by the gravity gradient. The tether array would radiate a single FMS wave. In the time-dependent background made of geomagnetic field plus radiated wave, plasma FMS perturbations are excited in the array vicinity through a parametric instability. The growth rate is estimated by truncating the evolution equation for FMS perturbations to the two azimuthal modes of lowest order. Design parameters such as tether length and number, required power and mass are discussed for Low Earth Orbit conditions. The array-attached wave structure would have the radiated wave controlled by the intensity and modulation frequency of the currents, making an active experiment on non-linear low frequency waves possible in real space plasma conditions.

Parametric study of the expansive joint model for cracking of concrete due to rebar corrosion

Un modelo numérico llamado elemento junta expansiva fue programado para simular la expansión mecánica del óxido y estudiar la fisuración en el hormigón circundante. El elemento junta expansiva trabaja con elementos finitos con fisura cohesiva embebida adaptable para simular la fractura del hormigón según el modelo de fisura cohesiva. Se ha comprobado que el modelo reproduce correctamente el patrón de fisuración del hormigón que se obtiene en ensayos de corrosión acelerada. En este trabajo, se realiza un estudio paramétrico del elemento junta expansiva para establecer los límites de los parámetros constitutivos del óxido. Se simula una cierta expansión variando los valores de los parámetros del óxido y se estudian la apertura de fisura y las tensiones resultantes en el hormigón. Se determina el rango de valores para los que los resultados de las simulaciones son prácticamente iguales, con el menor número posible de iteraciones.

O 1s excitation and ionization processes in the CO2 molecule studied via detection of low-energy fluorescence emission

Oxygen 1s excitation and ionization processes in the CO2 molecule have been studied with dispersed and non-dispersed fluorescence spectroscopy as well as with the vacuum ultraviolet (VUV) photon?photoion coincidence technique. The intensity of the neutral O emission line at 845 nm shows particular sensitivity to core-to-Rydberg excitations and core?valence double excitations, while shape resonances are suppressed. In contrast, the partial fluorescence yield in the wavelength window 300?650 nm and the excitation functions of selected O+ and C+ emission lines in the wavelength range 400?500 nm display all of the absorption features. The relative intensity of ionic emission in the visible range increases towards higher photon energies, which is attributed to O 1s shake-off photoionization. VUV photon?photoion coincidence spectra reveal major contributions from the C+ and O+ ions and a minor contribution from C2+. No conclusive changes in the intensity ratios among the different ions are observed above the O 1s threshold. The line shape of the VUV?O+ coincidence peak in the mass spectrum carries some information on the initial core excitation

Automatic Bandwidth Estimation Strategy for High-Quality Non-Parametric Modeling based Moving Object Detection

Here, a novel and efficient moving object detection strategy by non-parametric modeling is presented. Whereas the foreground is modeled by combining color and spatial information, the background model is constructed exclusively with color information, thus resulting in a great reduction of the computational and memory requirements. The estimation of the background and foreground covariance matrices, allows us to obtain compact moving regions while the number of false detections is reduced. Additionally, the application of a tracking strategy provides a priori knowledge about the spatial position of the moving objects, which improves the performance of the Bayesian classifier

Pushover analysis for the seismic response prediction of cable-stayed bridges under multi-directional excitation

Cable-stayed bridges represent nowadays key points in transport networks and their seismic behavior needs to be fully understood, even beyond the elastic range of materials. Both nonlinear dynamic (NL-RHA) and static (pushover) procedures are currently available to face this challenge, each with intrinsic advantages and disadvantages, and their applicability in the study of the nonlinear seismic behavior of cable-stayed bridges is discussed here. The seismic response of a large number of finite element models with different span lengths, tower shapes and class of foundation soil is obtained with different procedures and compared. Several features of the original Modal Pushover Analysis (MPA) are modified in light of cable-stayed bridge characteristics, furthermore, an extension of MPA and a new coupled pushover analysis (CNSP) are suggested to estimate the complex inelastic response of such outstanding structures subjected to multi-axial strong ground motions.

An efficient, parametric fixpoint algorithm for analysis of java bytecode

Abstract interpretation has been widely used for the analysis of object-oriented languages and, in particular, Java source and bytecode. However, while most existing work deals with the problem of flnding expressive abstract domains that track accurately the characteristics of a particular concrete property, the underlying flxpoint algorithms have received comparatively less attention. In fact, many existing (abstract interpretation based—) flxpoint algorithms rely on relatively inefHcient techniques for solving inter-procedural caligraphs or are speciflc and tied to particular analyses. We also argüe that the design of an efficient fixpoint algorithm is pivotal to supporting the analysis of large programs. In this paper we introduce a novel algorithm for analysis of Java bytecode which includes a number of optimizations in order to reduce the number of iterations. The algorithm is parametric -in the sense that it is independent of the abstract domain used and it can be applied to different domains as "plug-ins"-, multivariant, and flow-sensitive. Also, is based on a program transformation, prior to the analysis, that results in a highly uniform representation of all the features in the language and therefore simplifies analysis. Detailed descriptions of decompilation solutions are given and discussed with an example. We also provide some performance data from a preliminary implementation of the analysis.

An efficient, parametric fixpoint algorithm for incremental analysis of java bytecode

Abstract interpretation has been widely used for the analysis of object-oriented languages and, more precisely, Java source and bytecode. However, while most of the existing work deals with the problem of finding expressive abstract domains that track accurately the characteristics of a particular concrete property, the underlying fixpoint algorithms have received comparatively less attention. In fact, many existing (abstract interpretation based) fixpoint algorithms rely on relatively inefficient techniques to solve inter-procedural call graphs or are specific and tied to particular analyses. We argue that the design of an efficient fixpoint algorithm is pivotal to support the analysis of large programs. In this paper we introduce a novel algorithm for analysis of Java bytecode which includes a number of optimizations in order to reduce the number of iterations. Also, the algorithm is parametric in the sense that it is independent of the abstract domain used and it can be applied to different domains as "plug-ins". It is also incremental in the sense that, if desired, analysis data can be saved so that only a reduced amount of reanalysis is needed after a small program change, which can be instrumental for large programs. The algorithm is also multivariant and flowsensitive. Finally, another interesting characteristic of the algorithm is that it is based on a program transformation, prior to the analysis, that results in a highly uniform representation of all the features in the language and therefore simplifies analysis. Detailed descriptions of decompilation solutions are provided and discussed with an example.

Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser, is prevented when multiple plasma instabilities such as filamentation and hosing, and nonlinear coherent structures (vortices/post-solitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these insabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 {\mu}m (gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.

Swift heavy ion damage to sodium chloride: synergy between excitation and thermal spikes

Systematic data on the effect of irradiation with swift ions (Zn at 735 MeV and Xe at 929 MeV) on NaCl single crystals have been analysed in terms of a synergetic two-spike approach (thermal and excitation spikes). The coupling of the two spikes, simultaneously generated by the irradiation, contributes to the operation of a non-radiative exciton decay model as proposed for purely ionization damage. Using this scheme, we have accounted for the π-emission yield of self-trapped excitons and its temperature dependence under ion-beam irradiation. Moreover, the initial production rates of F-centre growth have also been reasonably simulated for irradiation at low temperatures ( < 100 K), where colour centre annealing and aggregation can be neglected.

Influence of Crystal Quality on the Excitation and Propagation of Surface and Bulk Acoustic Waves in Polycrystalline AlN Films

We investigate the excitation and propagation of acoustic waves in polycrystalline aluminum nitride films along the directions parallel and normal to the c-axis. Longitudinal and transverse propagations are assessed through the frequency response of surface acoustic wave and bulk acoustic wave devices fabricated on films of different crystal qualities. The crystalline properties significantly affect the electromechanical coupling factors and acoustic properties of the piezoelectric layers. The presence of misoriented grains produces an overall decrease of the piezoelectric activity, degrading more severely the excitation and propagation of waves traveling transversally to the c-axis. It is suggested that the presence of such crystalline defects in c-axis-oriented films reduces the mechanical coherence between grains and hinders the transverse deformation of the film when the electric field is applied parallel to the surface.

On the lateral excitation of shear modes in AlN layered resonators

In this paper we describe the fabrication and frequency characterization of different structures intended for the lateral excitation of shear modes in AlN c-axis-oriented films, which are at the same time designed to minimize the excitation of longitudinal modes. Laterally excited resonators were built on partially metallic (SiO2, W) and insulating (SiOC, Si3N4) acoustic mirrors built on silicon substrates, and on insulating mirrors (SiO2, TaOx) built on insulating glass plates. TiOx seed layers were used to stimulate the growth of highly c-axis oriented AlN films, which was confirmed by XRD and SAW measurements. Coplanar Mo electrodes of different geometries were defined on top of the AlN films to excite the shear modes. All the structures analyzed displayed a clear longitudinal mode, corresponding to an acoustic velocity of 11000 m/s, but a null or extremely weak shear response corresponding to a sound velocity of around 6350 m/s. The simulation of the frequency response based on Mason's model confirms that the shear resonance is extremely weak. The observed longitudinal modes are attributed either to the field applied between the electrodes and a conductive plane (metallic layer or Si substrate) or to the electric field parallel to the c-axis in the edges of the electrodes or in tilted grains. The low excitation of shear modes is attributed to the very low values of electric field strength parallel to the surface.

Parametric analysis of gravity offshore structures: Part 1

The objective of this paper is to analyse the influence of the variation of some parameters used in the analysis of the dynamic response of offshore structures under the action of wind generated waves. The structural response has been obtained by stochastic methods using two discretization models. One with lumped parameters, using translational degrees of freedom (d.o.f.) and the other with one-dimensional finite elements. Using each of these methods the problem has been solved with several d.o.f., analysing the influence of the number of d.o.f. on the results.

Study of the temperature distribution in Si nanowires under microscopic laser beam excitation

The use of laser beams as excitation sources for the characterization of semiconductor nanowires (NWs) is largely extended. Raman spectroscopy and photoluminescence (PL) are currently applied to the study of NWs. However, NWs are systems with poor thermal conductivity and poor heat dissipation, which result in unintentional heating under the excitation with a focused laser beam with microscopic size, as those usually used in microRaman and microPL experiments. On the other hand, the NWs have subwavelength diameter, which changes the optical absorption with respect to the absorption in bulk materials. Furthermore, the NW diameter is smaller than the laser beam spot, which means that the optical power absorbed by the NW depends on its position inside the laser beam spot. A detailed analysis of the interaction between a microscopic focused laser beam and semiconductor NWs is necessary for the understanding of the experiments involving laser beam excitation of NWs. We present in this work a numerical analysis of the thermal transport in Si NWs, where the heat source is the laser energy locally absorbed by the NW. This analysis takes account of the optical absorption, the thermal conductivity, the dimensions, diameter and length of the NWs, and the immersion medium. Both free standing and heat-sunk NWs are considered. Also, the temperature distribution in ensembles of NWs is discussed. This analysis intends to constitute a tool for the understanding of the thermal phenomena induced by laser beams in semiconductor NWs.

Detection and Isolation of Simultaneous Additive and Parametric Faults in Nonlinear Stochastic Dynamical Systems

This paper presents a new fault detection and isolation scheme for dealing with simultaneous additive and parametric faults. The new design integrates a system for additive fault detection based on Castillo and Zufiria, 2009 and a new parametric fault detection and isolation scheme inspired in Munz and Zufiria, 2008 . It is shown that the so far existing schemes do not behave correctly when both additive and parametric faults occur simultaneously; to solve the problem a new integrated scheme is proposed. Computer simulation results are presented to confirm the theoretical studies.

Automatic generation of real-time deformable parametric model of the aorta for a VR-based catheterism guidance system

The purpose of this work is twofold: first, to develop a process to automatically create parametric models of the aorta that can adapt to any possible intraoperative deformation of the vessel. Second, it intends to provide the tools needed to perform this deformation in real time, by means of a non-rigid registration method. This dynamically deformable model will later be used in a VR-based surgery guidance system for aortic catheterism procedures, showing the vessel changes in real time.