El motor i la transmissió del Fórmula Student BCN-001

El projecte que es presenta és en realitat un subprojecte d’un de global, que consisteix en la concepció, el disseny i la fabricació d’un prototip de monoplaça (el BCN‐001) per a participar, per primera vegada en la història de l’ETSEIB, en la prestigiosa competició universitària de la Formula Student. La part que aquí es descriu és la del motor i la transmissió. Es tracta d’un projecte real en el que s’ha aconseguit l’objectiu principal que era participar en la Formula Student 2007 celebrada al circuit de Silverstone (Anglaterra). L’abast del projecte no és tan sols teòric, amb simulacions i estudis, sinó també pràctic, amb la fabricació i muntatge de components. La cerca de proveïdors i patrocinadors també ha estat un treball important que ha comportat una dedicació d’un 50% del temps aproximadament. El disseny i l’elecció de cada component del cotxe està regit per una normativa estricte imposada per la competició. Quant a motor s’ha decidit muntar un Yamaha R6 de l’any 2005. Per normativa, el motor ha d’estar restringit per un brida de 20 mm de diàmetre situada entre la vàlvula papallona i la culata. Ha estat necessari el disseny d’una nova admissió fabricada en fibra de carboni. Els col∙lectors d’escapament també han estat dissenyats i manufacturats. Aquestes variacions respecte el motor original han comportat canviar la ECU que governa el motor per poder posar‐lo a punt. En la segona part del projecte es tracta la transmissió. La transmissió del BCN‐001 es composa d’un embragatge multidisc humit i d’una caixa de canvis seqüencial, integrats en mateix bloc del motor, una transmissió secundària per cadena, un diferencial autoblocant tipus torsen i les juntes homocinètiques i els paliers adaptats d’un Volkswagen Polo. Ha estat necessari el disseny de peces per tal d’acoblar tots aquests elements, així com el càlcul i elecció dels rodaments més adients

Thermal QRPA with Skyrme interactions and supernova neutral-current neutrino-nucleus reactions

The Thermal Quasiparticle Random-Phase Approximation is combined with the Skyrme energy density functional method (Skyrme-TQRPA) to study the response of a hot nucleus to an external perturbation. For the sample nuclei, $^{56}$Fe and $^{82}$Ge, the Skyrme-TQRPA is applied to analyze thermal effects on the strength function of charge-neutral Gamow-Teller transitions which dominate neutrino-nucleus reactions at $E_\nu \lesssim 20$~MeV. For the relevant supernova temperatures we calculate the cross sections for inelastic neutrino scattering. We also apply the method to examine the rate of neutrino-antineutrino pair emission by hot nuclei. The cross sections and rates are compared with those obtained earlier from the TQRPA calculations based on the phenomenological Quasiparticle-Phonon Model Hamiltonian. For inelastic neutrino scattering on $^{56}$Fe we also compare the Skyrme-TQRPA results to those obtained earlier from a hybrid approach that combines shell-model and RPA calculations.Comment: Minor revisions according to referee's recomendation

Gamow-Teller strength distributions at finite temperatures and electron capture in stellar environments

We propose a new method to calculate stellar weak-interaction rates. It is based on the Thermo-Field-Dynamics formalism and allows the calculation of the weak-interaction response of nuclei at finite temperatures. The thermal evolution of the GT$_+$ distributions is presented for the sample nuclei $^{54, 56}$Fe and ~$^{76,78,80}$Ge. For Ge we also calculate the strength distribution of first-forbidden transitions. We show that thermal effects shift the GT$_+$ centroid to lower excitation energies and make possible negative- and low-energy transitions. In our model we demonstrate that the unblocking effect for GT$_+$ transitions in neutron-rich nuclei is sensitive to increasing temperature. The results are used to calculate electron capture rates and are compared to those obtained from the shell model.Comment: 16 pages, 9 figure

In vitro and in vivo studies on the combination of Brequinar sodium (DUP-785; NSC 368390) with 5-fluorouracil; effects of uridine.

Brequinar sodium (DUP-785; Brequinar) is a potent inhibitor of the pyrimidine de novo enzyme dihydroorotate dehydrogenase (DHO-DH), leading to a depletion of pyrimidine nucleotides, which could be reversed by uridine. In in vitro studies we investigated the effect of different physiological concentrations of uridine on the growth-inhibition by Brequinar, the effect of the nucleoside transport inhibitor, dipyridamole, and the combination of Brequinar and 5-fluorouracil (5FU). Uridine at 1 microM slightly reversed the growth inhibition by Brequinar, while the effect of 5-500 microM was greater. However, at Brequinar concentrations greater than 30 microM, uridine could not reverse the growth-inhibitory effects. Addition of dipyridamole could only partially prevent the reversing effects of uridine. The combination of Brequinar and 5FU was more than additive in the absence of uridine in the culture medium, but not in the presence of uridine. The combination of Brequinar and 5FU was tested in vivo in two murine colon tumour models, Colon 26 and Colon 38. Scheduling of both compounds appeared to be very important. In Colon 38 no potentiating effect of Brequinar could be observed. In contrast in Colon 26 a more than additive effect could be observed. Since uridine concentrations are considerably different in these tumours (higher in Colon 38), it was concluded from both the in vitro and in vivo experiments that uridine is an important determinant in combinations of Brequinar and 5FU

R-process nucleosynthesis calculations with complete nuclear physics input

The r-process constitutes one of the major challenges in nuclear astrophysics. Its astrophysical site has not yet been identified but there is observational evidence suggesting that at least two possible sites should contribute to the solar system abundance of r-process elements and that the r-process responsible for the production of elements heavier than Z=56 operates quite robustly producing always the same relative abundances. From the nuclear-physics point of view the r-process requires the knowledge of a large number of reaction rates involving exotic nuclei. These include neutron capture rates, beta-decays and fission rates, the latter for the heavier nuclei produced in the r-process. We have developed for the first time a complete database of reaction rates that in addition to neutron-capture rates and beta-decay half-lives includes all possible reactions that can induce fission (neutron-capture, beta-decay and spontaneous fission) and the corresponding fission yields. In addition, we have implemented these reaction rates in a fully implicit reaction network. We have performed r-process calculations for the neutrino-driven wind scenario to explore whether or not fission can contribute to provide a robust r-process pattern

The Role of Fission in Neutron Star Mergers and Its Impact on the r-Process Peaks

Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree-Fock-Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.Peer reviewe

Q value and half-life of double-electron capture in Os-184

Os-184 has been excluded as a promising candidate for the search of neutrinoless double-electron capture. High-precision mass measurements with the Penning-trap mass spectrometer TRIGA-TRAP resulted in a marginal resonant enhancement with = -8.89(58) keV excess energy to the 1322.152(22) keV 0+ excited state in W-184. State-of-the-art energy density functional calculations are applied for the evaluation of the nuclear matrix elements to the excited states predicting a strong suppression due to the large deformation of mother and daughter states. The half-life of the transition in Os-184 exceeds T_{1/2} > 1.3 10^{29} years for an effective neutrino mass of 1 eV.Comment: accepted in Phys. Rev.