Factors determinants del temps de col·lecció de càrregues en una cambra de deriva

We study in this paper the resolution of a drift chamber, through the calculation of the drift time dependence on the ionizing particle position. In order to do so we calculate the electric field inside the chamber and we integrate the movement equation for the ionization - produced electrons. We conclude that the chamber response is non-linear for certain incident particle trajectories and that software corrections should be made in the off-line analysis

Quantum Monte Carlo estimation of complex-time correlations for the study of the ground-state dynamic structure function

We present a method based on the Path Integral Monte Carlo formalism for the calculation of ground-state time correlation functions in quantum systems. The key point of the method is the consideration of time as a complex variable whose phase $\delta$ acts as an adjustable parameter. By using high-order approximations for the quantum propagator, it is possible to obtain Monte Carlo data all the way from purely imaginary time to $\delta$ values near the limit of real time. As a consequence, it is possible to infer accurately the spectral functions using simple inversion algorithms. We test this approach in the calculation of the dynamic structure function $S(q,\omega)$ of two one-dimensional model systems, harmonic and quartic oscillators, for which $S(q,\omega)$ can be exactly calculated. We notice a clear improvement in the calculation of the dynamic response with respect to the common approach based on the inverse Laplace transform of the imaginary-time correlation function.Comment: Accepted for publication on "Jornal of Chemical Physics

Pràctiques de Laboratori

2015/201

Itinerant ferromagnetism in dilute SU(N) Fermi gases

We present exact analytic results for the energy of a SU(N) repulsive Fermi gas as a function of the spin-channel occupation at second order in the gas parameter. This is an extension of previous results that now incorporates the degree of polarization of the system. Therefore, the magnetic properties of the gas can be obtained, free from numerical uncertainties. For spin 1/2 we find that second-order corrections change the itinerant ferromagnetic transition from continuous to first-order. Instead, for spin larger than 1/2 the phase transition is always of first-order type. The transition critical density reduces when the spin increases, making the phase transition more accessible to experiments with ultracold dilute Fermi gases. Estimations for Fermi gases of Yb and Sr with spin 5/2 and 9/2, respectively, are reported

Itinerant ferromagnetism in dilute SU(N) Fermi gases

We present exact analytic results for the energy of a SU(N) repulsive Fermi gas as a function of the spin-channel occupation at second order in the gas parameter. This is an extension of an old result that now incorporates the degree of polarization of the system. Therefore, the magnetic properties of the gas can be obtained, free from numerical uncertainties. For spin 1/2 we find that second-order corrections change the itinerant ferromagnetic transition from continuous to first-order. Instead, for spin larger than 1/2 the phase transition is always of first-order type. The transition critical density reduces when the spin increases, making the phase transition more accessible to experiments with ultracold dilute Fermi gases. Estimations for Fermi gases of Yb and Sr with spin 5/2 and 9/2, respectively, are reported.Comment: 12 pages, 10 figures. New references adde

Beyond universality in repulsive SU(N) Fermi gases

Itinerant ferromagnetism in dilute Fermi gases is predicted to be at values of the gas parameter where second-order perturbation theory is not accurate enough. We have revisited perturbation theory up to third order for SU(N) fermions and found its generalization in terms of both the gas parameter and spin polarization. At difference with recent derivations of the same type at second-order, we have not been able to end up with a fully analytical result. Instead, we worked out analytically some of the terms and integrated numerically the rest. Our results agree satisfactorily with quantum Monte Carlo results for $s=1/2$ and hard-sphere interactions. For any value of the spin, we observe a discontinuous ferromagnetic transition but for $s=1/2$ the gap in the polarization at the transition is very small resembling more a quasi-continuous transition.Comment: 13 pages, 32 figure

Performance of growing-finishing pigs fed barley diets supplemented with different levels of beta-glucanase

Recent studies have been more concerned with enzymatic supplementation of diets for young pigs which digestive system is not yet well-developed, than for the fully-developed pig, where these growth promoters seem to have less effect on productive efficency of the animal. The aim of this work was to investigate if a B-glucanase supplementation affects the growing and fattening performances of pigs (EXP.l & EXP.2) and fecal digestibility (F.Dig) of dry matter (DM), crude protein (CP), fat (FAT), neutral detergent fiber (NDF), acid detergent fiber (ADF) and energy (E) (EXP 3.

Pràctiques de Laboratori

2015/201