Basin scale simulations of ocean acoustic tomography in the Portuguese exclusive economic zone

Rep. 03/02 - SiPLAB 16/October/2002This internal report describes some of the experiments developed in the eld of Ocean Acoustic Tomography, simulation results regarding the acoustic monitoring of the Portuguese Economic Exclussive Zone and a brief description of binary m-sequences

Hydrodynamical normal mode estimation on the INTIFANTE'00 data set

Rep 04/01 - SiPLAB 23/November/2001This report introduces a theoretical description of Dynamic Normal Modes, their relationship to temperature, salinity, and sound speed perturbations, and also of the numerical methods that allow the calculation of Dynamic Normal Modes

cTraceo User Manual

Rep. 01/12 - SiPLAB 10/January/2012This internal report describes the C port of the gaussian beam raytracing model TRACEO.This work was funded by National Funds through FCTFoundation for Science and Technology under project SENSOCEAN (PTDC/EEA_ELC/104561/2008)

A time-reversal suboptimal detector for underwater acoustic barriers

This paper proposes an experimental setup composed of two interconnected vertical arrays: one transmit only array (TOA) and a receive only array (ROA). It is shown that using the time reversal principle, where the ocean is used as a spatial matched filter, signal energy can be simultaneously focused on each ROA hydrophone and thus obtain the detector output by simple summation of the received energy over the array. This setup effectively configures a multistatic system with several transmitters and several receivers coherently processed both in time and space. Simulations using a ray trace propagation model combined with a naive scattering formulation show that the obtained empirical detection probability is close to the theoretical optimal bound derived assuming space - time white Gaussian noise. This system was tested in a sea trial that took place during September 2007 in the Hopav°agen Bay near Trondheim, Norway. The actual setup was composed of a 2 sources TOA on a shallow area of 8 m depth near the shore and a 16 receivers ROA approximately 100 m apart in a 8 to 25 m depth range dependent duct. The transmitted signals were 200 ms duration LFMs with 3 kHz bandwidths in two frequency bands centered on 5 and 10 kHz. The results obtained in realistic conditions show that a 1.7 m2 hard plate could be detected when placed across the barrier. Several results are presented and compared with the theoretical values. Although the system can be significantely improved, in particular by using more populated source and receiving arrays, it is believed that these results can be reproduced at sea in harbor like conditions

Estudio de correlación y variabilidad de los métodos de inmersión en mercurio y el método capacitivo resonante para determinar densidad aparente de material cerámico crudo

En el siguiente trabajo, se presentan los resultados del estudio de correlación de las variables y parámetros asociados a la medición de la Densidad Aparente (DAP) para material cerámico crudo utilizado en la fabricación industrial de baldosas para piso, frente al método de inmersión en mercurio. Los anteriores resultados se obtuvieron teniendo en cuenta la aplicación de un modelo matemático al DAP como función no lineal de parámetros como la temperatura, permitividad eléctrica relativa y variables como la humedad relativa HR, voltaje y frecuencia de resonancia, medidos con un dispositivo electrónico diseñado en la Universidad Central por el grupo de investigación en Estado Sólido y Optoelectrónica ESSOPTO y utilizado en el Centro de Investigación en Materiales Cerámicos de la UFPS – CIMAC de la Universidad Francisco de Paula Santander – Cúcuta Colombia.Peer reviewe

Range-dependent regularization of travel-time tomography based on theoretical modes

Travel time inversion is a fundamental method of Ocean Acoustic Tomography, for the estimation of perturbations in sound speed. By discretizing the watercolumn into a system of layers, the method allows to introduce a system of linear equations, relating a known vector of perturbations in travel time, to an unknown vector of perturbations in sound speed, through the so-called \observation matrix". Inverting the system allows to determine a solution, which estimates the perturbation in sound speed in each layer of the watercolumn. However, in most problems of practical interest, the number of unknowns (i.e. the perturbations in sound speed) is larger that the number of equations (which correspond to the number of delays in travel time), which implies that inverting the system of linear equations can be viewed as an ill-posed problem. The discussion presented in this paper illustrates an approach to the problem of inversion, which is based on the usage of theoretical modes. Further, it is shown that for a range-dependent perturbation in sound speed, which corresponds to a superposition of plane waves, the inversion problem can be regularized (i.e. the system of linear equations can be rewritten in order to deal with more equations than unknowns) by estimating only the amplitudes and phases of the linear waves. Particular examples are given for simulated and real data

Decay of low-lying 12C resonances within a 3alpha cluster model

We compute energy distributions of three $\alpha$-particles emerging from the decay of $^{12}$C resonances by means of the hyperspherical adiabatic expansion method combined with complex scaling. The large distance continuum properties of the wave functions are crucial and must be accurately calculated. The substantial changes from small to large distances determine the decay mechanisms. We illustrate by computing the energy distributions from decays of the $1^{+}$ and $3^-$-resonances in $^{12}$C. These states are dominated by direct and sequential decays into the three-body continuum respectively.Comment: 5 pages, 3 figures. Proceedings of the Clusters '07 conference held in Stratford-upon-Avon in September 200

Gluon propagator, triple gluon vertex and the QCD coupling constant

We study the UV-scaling of the flavorless gluon propagator in the Landau gauge in an energy window up to 9 GeV. Dominant hypercubic lattice artifacts are eliminated. A large set of renormalization schemes is used to test asymptotic scaling. We compare with our results obtained directly from the triple gluon vertex. We end-up with \Lambda_{\bar{\rm{MS}}} = 318(12)(5) MeV and 292(5)(15) MeV respectively for these two methods, compatible which each other but significantly above the Schrodinger method estimate.Comment: 3 pages, LaTeX with two figures; presented at LATTICE9

HS 1857+5144 : a hot and young pre-cataclysmic variable

Aims. We report the discovery of a new white dwarf/M dwarf binary, HS 1857+5144, identified in the Hamburg Quasar Survey (HQS). Methods. Time-resolved optical spectroscopy and photometry were carried out to determine the properties of this new cataclysmic variable progenitor (pre-CV). Results. The light curves of HS 1857+5144 display a sinusoidal variation with a period of Porb = 383.52 min and peak-to-peak amplitudes of 0.7 mag and 1.1mag in the B-band and R-band, respectively. The large amplitude of the brightness variation results from a reflection effect on the heated inner hemisphere of the companion star, suggesting a very high temperature of the white dwarf. Our radial velocity study confirms the photometric period as the orbital period of the system. A model atmosphere fit to the spectrum of the white dwarf obtained at minimum light provides limits to its mass and temperature of Mwd 0.6−1.0 M and Twd 70 000−100 000 K, respectively. The detection of He II λ4686 absorption classifies the primary star of HS 1857+5144 as a DAO white dwarf. Combining the results from our spectroscopy and photometry, we estimate the mass of the companion star and the binary inclination to be Msec 0.15−0.30 M and i 45◦−55◦, respectively. Conclusions. We classify HS 1857+5144 as one of the youngest pre-CV known to date. The cooling age of the white dwarf suggests that the present system has just emerged from a common envelope phase ∼105 yr ago. HS 1857+5144 will start mass transfer within or below the 2–3 h period gap

Influence of MWCNT/surfactant dispersions on the mechanical properties of Portland cement pastes

This work studies the reinforcing effect of Multi Walled Carbon Nanotubes (MWCNT) on cement pastes. A 0.35% solid concentration of MWCNT in powder was dispersed in deionized water with sodium dodecyl sulfate (cationic surfactant), cetylpyridinium chloride (anionic surfactant) and triton X-100 (amphoteric surfactant) using an ultrasonic tip processor. Three concentrations of each surfactant (1mM, 10mM and 100mM) were tested, and all samples were sonicated until an adequate dispersion degree was obtained. Cement pastes with additions of carbon nanotubes of 0.15% by mass of cement were produced in two steps; first the dispersions of MWCNT were combined with the mixing water using an ultrasonic tip processor to guarantee homogeneity, and then cement was added and mixed until a homogeneous paste was obtained. Direct tensile strength, apparent density and open porosity of the pastes were measured after 7 days of curing. It was found that the MWCNT/surfactants dispersions decrease the mechanical properties of the cement based matrix due to an increased porosity caused by the presence of surfactants. © Published under licence by IOP Publishing Ltd