A Spitzer Study of Interacting Luminous and Ultra-Luminous Infrared Galaxies

We conducted a Spitzer Space Telescope survey of 28 Luminous (11 < log(LIR/L_odot) < 12, LIRGs) and Ultra-Luminous Infrared Galaxies (log(LIR/L_odot) > 12, ULIRGs). Many of these galaxies are found in pairs or associations and are powered by either nuclear activity or starformation (Sanders & Mirabel 1996). Our main goal is to understand the relative importance of starbursts and AGNs in interacting systems. Is the frequency of AGN and starbursts in these interacting galaxies related to their luminosities? What is the importance of the merger stage and the frequency of AGNs? We present our conclusions and diagnostic diagrams based in the observed near infrared lines and compare to studies based solely in optical data.Comment: 3 pages, 2 figures, to appear in the Spectral Energy Distribution of Galaxies (SED2011) conference proceedings, Preston, UK, 201

On the Price of German Treasury Bills

In this paper, we examine the primary and secondary markets for German treasury bills. We look in great detail at the rationale behind banks’ decisions concerning the yield they require to be willing to buy treasury bills in the primary market; and we also mention the reasoning behind household and nonbank firm decisions concerning the price they are willing to pay to buy these bills in the secondary market. We use data from real world tenders to show that the bids set by banks conform to what our theoretical framework would predict. In particular, we show that current monetary policy and the markets’ expectations regarding its future path can be used to define a range where the banks bids lie.FC

Wavelets: a powerful tool for studying rotation, activity, and pulsation in Kepler and CoRoT stellar light curves

Aims. The wavelet transform has been used as a powerful tool for treating several problems in astrophysics. In this work, we show that the time-frequency analysis of stellar light curves using the wavelet transform is a practical tool for identifying rotation, magnetic activity, and pulsation signatures. We present the wavelet spectral composition and multiscale variations of the time series for four classes of stars: targets dominated by magnetic activity, stars with transiting planets, those with binary transits, and pulsating stars. Methods. We applied the Morlet wavelet (6th order), which offers high time and frequency resolution. By applying the wavelet transform to the signal, we obtain the wavelet local and global power spectra. The first is interpreted as energy distribution of the signal in time-frequency space, and the second is obtained by time integration of the local map. Results. Since the wavelet transform is a useful mathematical tool for nonstationary signals, this technique applied to Kepler and CoRoT light curves allows us to clearly identify particular signatures for different phenomena. In particular, patterns were identified for the temporal evolution of the rotation period and other periodicity due to active regions affecting these light curves. In addition, a beat-pattern signature in the local wavelet map of pulsating stars over the entire time span was also detected.Comment: Accepted for publication on A&

A contribution to the study of the German treasury bills market

We study the yields in the German treasury bills market. We take a detailed look at the yield banks require to buy treasury bills in the primary market, and we also examine the yield households and nonbank firms demand to buy these bills in the secondary market. We use data from real world tenders to show that the bids set by banks are in accordance with the predictions of our theoretical framework. In particular, we show that current monetary policy and the market's expectations regarding the future path of monetary policy can be used to define an interval in which the bids from banks lie. Our theoretical predictions for the secondary market also match the data.info:eu-repo/semantics/publishedVersio

Transient Charging and Discharging of Spin-polarized Electrons in a Quantum Dot

We study spin-polarized transient transport in a quantum dot coupled to two ferromagnetic leads subjected to a rectangular bias voltage pulse. Time-dependent spin-resolved currents, occupations, spin accumulation, and tunneling magnetoresistance (TMR) are calculated using both nonequilibrium Green function and master equation techniques. Both parallel and antiparallel leads' magnetization alignments are analyzed. Our main findings are: a dynamical spin accumulation that changes sign in time, a short-lived pulse of spin polarized current in the emitter lead (but not in the collector lead), and a dynamical TMR that develops negative values in the transient regime. We also observe that the intra-dot Coulomb interaction can enhance even further the negative values of the TMR.Comment: 7 pages, 6 figures. Typos corrections corresponding to the published versio