Nonlinear dynamo models using quasi-biennial oscillations constrained by sunspot area data

Contex: Solar magnetic activity exhibits variations with periods between 1.5--4 years, the so-called quasi-biennial oscillations (QBOs), in addition to the well-known 11-year Schwabe cycles. Solar dynamo is thought to be the responsible mechanism for generation of the QBOs. Aims: In this work, we analyse sunspot areas to investigate the spatial and temporal behaviour of the QBO signal and study the responsible physical mechanisms using simulations from fully nonlinear mean-field flux-transport dynamos. Methods: We investigated the behaviour of the QBOs in the sunspot area data in full disk, and northern and southern hemispheres, using wavelet and Fourier analyses. We also ran solar dynamos with two different approaches to generating a poloidal field from an existing toroidal field, Babcock-Leighton and turbulent $\alpha$ mechanisms. We then studied the simulated magnetic field strengths as well as meridional circulation and differential rotation rates using the same methods. Results: The results from the sunspot areas show that the QBOs are present in the full disk and hemispheric sunspot areas and they show slightly different spatial and temporal behaviours, indicating a slightly decoupled solar hemispheres. The QBO signal is generally intermittent and in-phase with the sunspot area data, surfacing when the solar activity is in maximum. The results from the BL-dynamos showed that they are neither capable of generating the slightly decoupled behaviour of solar hemispheres nor can they generate QBO-like signals. The turbulent $\alpha$-dynamos, on the other hand, generated decoupled hemispheres and some QBO-like shorter cycles. Conclusions: In conclusion, our simulations show that the turbulent $\alpha$-dynamos with the Lorentz force seems more efficient in generating the observed temporal and spatial behaviour of the QBO signal compared with those from the BL-dynamos

Search for the Standard Model Higgs boson in decays in H → τ+τ− proton-proton collisions with the ATLAS detector

The status of the search for the Standard Model (SM) Higgs decaying into a τ pair is reported. The analysis is based on the proton-proton data collected with the ATLAS detector corresponding to integrated luminosities of 4.6 fb−1 and 13.0 fb−1 at centre-of-mass energies of √s = 7TeV and 8TeV, respectively. The observed (expected) upper limit at 95% CL on the σ × BR for SM H → τ+τ− is found to be 1.9 (1.2) × SM prediction for mH = 125 GeV. For this Higgs mass the observed (expected) deviation for the background only hypothesis corresponds to a local significance of 1.1 (1.7) standard deviations

Acoustic power absorption and enhancement generated by slow and fast MHD waves

We used long duration, high quality, unresolved (Sun-as-a star) observations collected by the ground based network BiSON and by the instruments GOLF and VIRGO on board the ESA/NASA SOHO satellite to search for solar-cycle-related changes in mode characteristics in velocity and continuum intensity for the frequency range between 2.5mHz < nu < 6.8mHz. Over the ascending phase of solar cycle 23 we found a suppression in the p-mode amplitudes both in the velocity and intensity data between 2.5mHz <nu< 4.5mHz with a maximum suppression for frequencies in the range between 2.5mHz <nu< 3.5mHz. The size of the amplitude suppression is 13+-2 per cent for the velocity and 9+-2 per cent for the intensity observations. Over the range 4.5mHz <nu< 5.5mHz the findings hint within the errors to a null change both in the velocity and intensity amplitudes. At still higher frequencies, in the so called High-frequency Interference Peaks (HIPs) between 5.8mHz <nu < 6.8mHz, we found an enhancement in the velocity amplitudes with the maximum 36+-7 per cent occurring for 6.3mHz <nu< 6.8mHz. However, in intensity observations we found a rather smaller enhancement of about 5+-2 per cent in the same interval. There is evidence that the frequency dependence of solar-cycle velocity amplitude changes is consistent with the theory behind the mode conversion of acoustic waves in a non-vertical magnetic field, but there are some problems with the intensity data, which may be due to the height in the solar atmosphere at which the VIRGO data are taken.Comment: Accepted for publication in A&A. 10 pages, 9 figures

Una clase en el laboratorio de matemática como objeto de investigación

El trabajo refiere a experiencias realizadas en el aula con alumnos universitarios de primer año de estudios de una carrera de Ingeniería de la Facultad Regional Santa Fe de la Universidad Tecnológica Nacional durante el desarrollo de una Unidad didáctica de Matemática. Uno de los objetivos que nos planteamos consiste en analizar las respuestas de los alumnos cuando, a través de la estrategia pedagógica especialmente diseñada, se le proporciona la oportunidad de construir sus propias ideas para lograr la comprensión de ciertos conceptos. Un aspecto del diseño es la inclusión de la herramienta computacional DERIVE como herramienta cognitiva que permite colaborar con el alumno en la exploración, organización y representación del conocimiento matemático y como un valioso instrumento para el aprendizaje de Geometría. La experiencia consistió en la observación y descripción de las selecciones de los alumnos ante situaciones concretas planteadas en el proceso de construcción del conocimiento

The Quasi-Biennial Periodicity (QBP) in velocity and intensity helioseismic observations

We looked for signatures of Quasi-Biennial Periodicity (QBP) over different phases of solar cycle by means of acoustic modes of oscillation. Low-degree p-mode frequencies are shown to be sensitive to changes in magnetic activity due to the global dynamo. Recently have been reported evidences in favor of two-year variations in p-mode frequencies. Long high-quality helioseismic data are provided by BiSON (Birmingham Solar Oscillation Network), GONG (Global Oscillation Network Group), GOLF (Global Oscillation at Low Frequency) and VIRGO (Variability of Solar IRradiance and Gravity Oscillation) instruments. We determined the solar cycle changes in p-mode frequencies for spherical degree l=0, 1, 2 with their azimuthal components in the frequency range 2.5 mHz < nu < 3.5 mHz. We found signatures of QBP at all levels of solar activity in the modes more sensitive to higher latitudes. The signal strength increases with latitude and the equatorial component seems also to be modulated by the 11-year envelope. The persistent nature of the seismic QBP is not observed in the surface activity indices, where mid-term variations are found only time to time and mainly over periods of high activity. This feature together with the latitudinal dependence provides more evidences in favor of a mechanism almost independent and different from the one that brings up to the surface the active regions. Therefore, these findings can be used to provide more constraints on dynamo models that consider a further cyclic component on top of the 11-year cycle.Comment: 9 pages, 9 Figures, 2 Tables Accepted for publication in A&