Nonlinear Interaction of Transversal Modes in a CO2 Laser

We show the possibility of achieving experimentally a Takens-Bogdanov bifurcation for the nonlinear interaction of two transverse modes ($l = \pm 1$) in a $CO_2$ laser. The system has a basic O(2) symmetry which is perturbed by some symmetry-breaking effects that still preserve the $Z_2$ symmetry. The pattern dynamics near this codimension two bifurcation under such symmetries is described. This dynamics changes drastically when the laser properties are modified.Comment: 16 pages, 0 figure

Molecular Gastronomy in Spain

[EN] Beyond the overwhelming international success of Ferrán Adria, Spain has been one of the countries with a more active implication in molecular gastronomy as a scientific discipline but also in the use of ingredients, technologies, and equipment from the scientificand technological universe in the culinary area. Nowadays, this is a well-established discipline in Spain, with a number of research groups covering related topics, several companies commercializing appliances and additives worldwide, and renowned international chefs and many restaurants and companies committed to the collaboration with scientists for facing the future of Spanish gastronomyThe authors would like to thank the Ministerio de Ciencia e Innovación (Spain) for funding the Collaborative Network “INDAGA” (AGL2007-28589- E/ALI; AGL2009-05765-E), which enabled their collaboration.García Segovia, P.; Garrido, MD.; Vercet Tormo, A.; Arboleya, JC.; Fiszman Dal Santo, S.; Martínez Monzó, J.; Laguarda, S.... (2014). Molecular Gastronomy in Spain. Journal of Culinary Science and Technology. 12(4):279-293. https://doi.org/10.1080/15428052.2014.914813S27929312

Steady state representation of the homogeneous cooling state of a granular gas

The properties of a dilute granular gas in the homogeneous cooling state are mapped to those of a stationary state by means of a change in the time scale that does not involve any internal property of the system. The new representation is closely related with a general property of the granular temperature in the long time limit. The physical and practical implications of the mapping are discussed. In particular, simulation results obtained by the direct simulation Monte Carlo method applied to the scaled dynamics are reported. This includes ensemble averages and also the velocity autocorrelation function, as well as the self-diffusion coefficient obtained from the latter by means of the Green-Kubo representation. In all cases, the obtained results are compared with theoretical predictions

Gaseous time projection chambers for rare event detection: Results from the T-REX project. II. Dark matter

As part of the T-REX project, a number of R&D and prototyping activities have been carried out during the last years to explore the applicability of Micromegas-read gaseous TPCs in rare event searches like double beta decay (DBD), axion research and low-mass WIMP searches. While in the companion paper we focus on DBD, in this paper we focus on the results regarding the search for dark matter candidates, both axions and WIMPs. Small ultra-low background Micromegas detectors are used to image the x-ray signal expected in axion helioscopes like CAST at CERN. Background levels as low as $0.8\times 10^{-6}$ c keV$^{-1}$cm$^{-2}$s$^{-1}$ have already been achieved in CAST while values down to $\sim10^{-7}$ c keV$^{-1}$cm$^{-2}$s$^{-1}$ have been obtained in a test bench placed underground in the Laboratorio Subterr\'aneo de Canfranc. Prospects to consolidate and further reduce these values down to $\sim10^{-8}$ c keV$^{-1}$cm$^{-2}$s$^{-1}$will be described. Such detectors, placed at the focal point of x-ray telescopes in the future IAXO experiment, would allow for 10$^5$ better signal-to-noise ratio than CAST, and search for solar axions with $g_{a\gamma}$ down to few 10$^{12}$ GeV$^{-1}$, well into unexplored axion parameter space. In addition, a scaled-up version of these TPCs, properly shielded and placed underground, can be competitive in the search for low-mass WIMPs. The TREX-DM prototype, with $\sim$0.300 kg of Ar at 10 bar, or alternatively $\sim$0.160 kg of Ne at 10 bar, and energy threshold well below 1 keV, has been built to test this concept. We will describe the main technical solutions developed, as well as the results from the commissioning phase on surface. The anticipated sensitivity of this technique might reach $\sim10^{-44}$ cm$^2$ for low mass ($<10$ GeV) WIMPs, well beyond current experimental limits in this mass range.Comment: Published in JCAP. New version with erratum incorporated (new figure 14

Large quantum nonlinear dynamic susceptibility of single-molecule magnets

The nonlinear dynamical response of Mn$_{12}$ single-molecule magnets is experimentally found to be very large, quite insensitive to the spin-lattice coupling constant, and displaying peaks reversed with respect to classical superparamagnets. It is shown that these features are caused by the strong field dependence of the relaxation rate due to the detuning of energy levels between which tunneling takes place. The nonlinear susceptibility technique, previously overlooked, is thus proposed as a privileged probe to ascertain the occurrence of quantum effects in mesoscopic magnetic systems.Comment: 4 pages, 4 figure

Lessons from the operation of the "Penning-Fluorescent" TPC and prospects

We have recently reported the development of a new type of high-pressure Xenon time projection chamber operated with an ultra-low diffusion mixture and that simultaneously displays Penning effect and fluorescence in the near-visible region (300 nm). The concept, dubbed `Penning-Fluorescent' TPC, allows the simultaneous reconstruction of primary charge and scintillation with high topological and calorimetric fidelity

The Bose–Hubbard model with squeezed dissipation

The stationary properties of the Bose–Hubbard model under squeezed dissipation are investigated. The dissipative model does not possess aU (1) symmetry but conserves parity. We find that 〈a j 〉 = 0 always holds, so no symmetry breaking occurs. Without the onsite repulsion, the linear case is known to be critical. At the critical point the system freezes to an EPR state with infinite two mode entanglement. We show here that the correlations are rapidly destroyed whenever the repulsion is switched on. As we increase the latter, the system approaches a thermal state with an effective temperature defined in terms of the squeezing parameter in the dissipators. We characterize this transition by means of a Gutzwiller ansatz and the Gaussian Hartree–Fock–Bogoliubov approximation

A Transitional Year Level to Higher Education: Challenges, Experiences and Self-regulatory Strategies during the Final Year of the University Preparatory Level

Final Year level of the University Preparatory cycle (FYUP) –in Spanish 2º Bachillerato– is one of the most challenging academic courses. It is extremely demanding academically in itself and by the end of it students must also pass the university entry exam. Yet research has not investigated how students experience this year. We thus explored, using in-depth interviews with 75 students from two public high schools, their attitudes toward this academic year. Our results showed that (a) the participants struggled greatly during FYUP, experiencing high levels of academic stress (that affects their general well-being, mostly because of the high academic demands); (b) students were looking forward to their university experience but were concerned about failing or not finding their place; and (c) they reported a narrow range of learning, motivational, and emotional strategies. This study shows that students face significant learning and academic challenges during FYUP. A clear educational implication is that interventions should be implemented in earlier years to help the students be better prepared

Hydrodynamic modes, Green-Kubo relations, and velocity correlations in dilute granular gases

It is shown that the hydrodynamic modes of a dilute granular gas of inelastic hard spheres can be identified, and calculated in the long wavelength limit. Assuming they dominate at long times, formal expressions for the Navier-Stokes transport coefficients are derived. They can be expressed in a form that generalizes the Green-Kubo relations for molecular systems, and it is shown that they can also be evaluated by means of $N$-particle simulation methods. The form of the hydrodynamic modes to zeroth order in the gradients is used to detect the presence of inherent velocity correlations in the homogeneous cooling state, even in the low density limit. They manifest themselves in the fluctuations of the total energy of the system. The theoretical predictions are shown to be in agreement with molecular dynamics simulations. Relevant related questions deserving further attention are pointed out