Calibration systems of the ANTARES neutrino telescope

The ANTARES detector is the largest deep sea underwater neutrino telescope in operation. The apparatus comprises a matrix of 885 photomultiplier tubes (PMTs) which detect the Cherenkov light emitted by the charged leptons produced in the charged current interactions of high energy neutrinos with the matter inside or near the detector. Reconstruction of the muon track and energy can be achieved using the time, position and charge information of the hits arriving to the PMTs. A good calibration of the detector is necessary in order to ensure its optimal performance. This contribution reviews the different calibration systems and methods developed by the ANTARES Collaboration.Comment: Contribution to VLvNT 2011, to be published in NIM A, 4 pages, 7 figure

Broadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5_{0.5}Sr1.5_{1.5}Co2_2Fe12_{12}O22{22}

Single phase multiferroics in which ordered magnetic and ferroelectricity coexist, are of great interest for new multifunctional devices, and among them Y-type hexaferrites are good candidates. Transverse susceptibility measurements, which have been proved to be a versatile tool to study singular properties of bulk and nanoparticle magnetic systems, have been carried out with a broadband system on polycrystalline Y type hexaferrites with composition Ba$_{0.5}$Sr$_{1.5}$Co$_2$Fe$_{12}$O${22}$, optimal to exhibit multiferroic properties. In the temperature range 80-350 K transverse susceptibility measurements with DC fields up to $\pm$5000 Oe reveal different behaviour depending on the sintering temperature. The thermal evolution of the anisotropy field peak exhibit four regions with different slopes: positive in 80-130 K, negative in 130-200 K, constant in 200-280 K and negative in 280-350 K, which can be considered a signature of spin transitions in this compound.Comment: arXiv admin note: substantial text overlap with arXiv:2401.1614

Using synchronization to improve earthquake forecasting in a cellular automaton model

A new forecasting strategy for stochastic systems is introduced. It is inspired by the concept of anticipated synchronization between pairs of chaotic oscillators, recently developed in the area of Dynamical Systems, and by the earthquake forecasting algorithms in which different pattern recognition functions are used for identifying seismic premonitory phenomena. In the new strategy, copies (clones) of the original system (the master) are defined, and they are driven using rules that tend to synchronize them with the master dynamics. The observation of definite patterns in the state of the clones is the signal for connecting an alarm in the original system that efficiently marks the impending occurrence of a catastrophic event. The power of this method is quantitatively illustrated by forecasting the occurrence of characteristic earthquakes in the so-called Minimalist Model.Comment: 4 pages, 3 figure

High-dimensional decoy-state quantum key distribution over 0.3 km of multicore telecommunication optical fibers

Multiplexing is a strategy to augment the transmission capacity of a communication system. It consists of combining multiple signals over the same data channel and it has been very successful in classical communications. However, the use of enhanced channels has only reached limited practicality in quantum communications (QC) as it requires the complex manipulation of quantum systems of higher dimensions. Considerable effort is being made towards QC using high-dimensional quantum systems encoded into the transverse momentum of single photons but, so far, no approach has been proven to be fully compatible with the existing telecommunication infrastructure. Here, we overcome such a technological challenge and demonstrate a stable and secure high-dimensional decoy-state quantum key distribution session over a 0.3 km long multicore optical fiber. The high-dimensional quantum states are defined in terms of the multiple core modes available for the photon transmission over the fiber, and the decoy-state analysis demonstrates that our technique enables a positive secret key generation rate up to 25 km of fiber propagation. Finally, we show how our results build up towards a high-dimensional quantum network composed of free-space and fiber based linksComment: Please see the complementary work arXiv:1610.01812 (2016

Neutral magic-angle bilayer graphene: Condon instability and chiral resonances

We discuss the full optical response of twisted bilayer graphene at the neutrality point close to the magic angle within the continuum model. (i) First, we define the full optical response consistent with the underlying $D_3$ symmetry, yielding the total, magnetic, and chiral response that transform according to the irreducible representations $A_1$, $A_2$, and $E$, respectively. Then, we numerically calculate the dissipative and reactive response for twist angles around the magic angle $\theta_m$ and comment on the possibility of a Condon instability. (ii) Second, we numerically calculate the full optical response {\it almost at} $\theta_m$. The total response is characterized by three universal plateaus which can be obtained from an analytical calculation. The magnetic and the chiral response, however, is given by corresponding non-universal plateaus depending on the twist angle $\theta$ via the dimensionless parameter $\alpha\sim\theta_m-\theta$. (iii) Following the discussion on the large magnetic response, we calculate the plasmonic excitations at the neutrality point inside the optical gap of relaxed twisted bilayer graphene. We find that acoustic plasmons extend over almost the whole optical gap and carry the largest oscillator strength. (iv) Finally, we discuss symmetry relations for the response functions as function of the chemical potential and highlight the consequences of the approximate particle-hole symmetry of the continuum model for twisted bilayer graphene. We then discuss a detailed balance relation where the chiral response at charge neutrality can be understood in terms of electron (hole) transitions for which the initial (final) states are energetically closer to charge neutrality than the final (initial) states.Comment: 17 pages, 7 figure

Actividad antibacteriana de quince antibióticos frente a enterobacterias aisladas en otitis externas caninas crónicas

Hemos estudiado la sensibilidad a quince antimicrobianos de las enterobacterias aisladas en otitis externas caninas crónicas. Se analizaron 20 cepas: 10 Proteus mirabilis, 9 Eseheriehia coli y 1 Klebsiella oxytoca. Se observaron diferencias en sensibilidad en función del género. Todas las cepas de enterobacterias fueron sensibles a ceftazidima, cefoxitina, gentamicina y netilmicina. Todas las cepas de Proteus mirabilis fueron sensibles además a amikacina, cefotaxima, piperacilina, ticarcilina, ciprofloxacina, enrofloxacina y marbofloxacina. En el caso de E. coli, todas las cepas fueron sensibles a tobramicina, además de a los 4 antibióticos descritos para el totaí de entero bacterias. La cepa de Klebsiella oxytoea fue sensible a 13 de los antibióticos estudiados, presentando una sensibilidad intermedia a piperacilina y siendo resistente a ticarcilina. Se realizaron encuestas alos veterinarios clínicos sobre los tratamientos que utilizaban para comparar nuestros resultados con la práctica clínica. Nuestros resultados apoyan la importancia de los ensayos de sensibilidad a antimicrobianos en las infeccionesen animales y sugieren que la gentamicina podría ser, en nuestra área, el antibiótico de elección para otitisexternas caninas crónicas causadas por enterobacterias

Internal and external variability in regional simulations of the Iberian Peninsula climate over the last millennium

In this study we analyse the role of internal variability in regional climate simulations through a comparison of two regional paleoclimate simulations for the last millennium. They share the same external forcings and model configuration, differing only in the initial condition used to run the driving global model simulation. A comparison of these simulations allows us to study the role of internal variability in climate models at regional scales, and how it affects the long-term evolution of climate variables such as temperature and precipitation. The results indicate that, although temperature is homogeneously sensitive to the effect of external forcings, the evolution of precipitation is more strongly governed by random unpredictable internal dynamics. There are, however, some areas where the role of internal variability is lower than expected, allowing precipitation to respond to the external forcings. In this respect, we explore the underlying physical mechanisms responsible for it. This study identifies areas, depending on the season, in which a direct comparison between model simulations of precipitation and climate reconstructions would be meaningful, but also other areas where good agreement between them should not be expected even if both are perfect

New Algebraic Quantum Many-body Problems

We develop a systematic procedure for constructing quantum many-body problems whose spectrum can be partially or totally computed by purely algebraic means. The exactly-solvable models include rational and hyperbolic potentials related to root systems, in some cases with an additional external field. The quasi-exactly solvable models can be considered as deformations of the previous ones which share their algebraic character.Comment: LaTeX 2e with amstex package, 36 page