Superheavy nuclei in relativistic effective Lagrangian model

Isotopic and isotonic chains of superheavy nuclei are analyzed to search for spherical double shell closures beyond Z=82 and N=126 within the new effective field theory model of Furnstahl, Serot, and Tang for the relativistic nuclear many-body problem. We take into account several indicators to identify the occurrence of possible shell closures, such as two-nucleon separation energies, two-nucleon shell gaps, average pairing gaps, and the shell correction energy. The effective Lagrangian model predicts N=172 and Z=120 and N=258 and Z=120 as spherical doubly magic superheavy nuclei, whereas N=184 and Z=114 show some magic character depending on the parameter set. The magicity of a particular neutron (proton) number in the analyzed mass region is found to depend on the number of protons (neutrons) present in the nucleus.

Shell structure in mixed 3He-4He droplets

Due to the immiscibility of 3He into 4He at very low temperatures, mixed helium droplets consist of a core of 4He atoms coated by a 3He layer whose thickness depends on the number of atoms of each isotope. When these numbers are such that the centrifugal kinetic energy of the 3He atoms is small and can be considered as a perturbation to the mean-field energy, a novel shell structure arises, with magic numbers different from these of pure 3He droplets. If the outermost shell is not completely filled, the valence atoms align their spins up to the maximum value allowed by the Pauli principle.

Moral Hazard in Repeated Procurement of Services

This paper analyzes repeated procurement of services as a four-stage game divided into two periods. In each period there is (1) a contest stage à la Tullock in which the principal selects an agent and (2) a service stage in which the selected agent provides a service. Since this service effort is non-verifiable, the principal faces a moral hazard problem at the service stages. This work considers how the principal should design the period-two contest to mitigate the moral hazard problem in the period-one service stage and to maximize total service and contest efforts. It is shown that the principal must take account of the agent's past service effort in the period-two contest success function. The results indicate that the optimal way to introduce this `bias' is to choose a certain degree of complementarity between past service and current contest efforts. This result shows that contests with `additive bias' (`multiplicative bias') are optimal in incentive problems when effort cost is low (high). Furthermore, it is shown that the severity of the moral hazard problem increases with the cost of service effort (compared to the cost of contest effort) and the number of agents. Finally, the results are extended to more general contest success functions. JEL classification: C72; D82 Key words: Biased contests; Moral Hazard; Repeated Game; Incentives.

Young people and youth policies in Spain in times of austerity: between juggling and the trapeze

The aim of this article is to present and discuss the situation regarding young people and youth policy in Spain via the parameters of the magic triangle linking policy, research and action: (1) the situation of young people in Spain today -some indicators are highlighted regarding the main challenges and opportunities for young people, with references to the so-called"Ni-Nis" (neither studying nor working)- and the movement of the"outraged" youth that occupied the streets of Spain"s major cities in May 2011; (2) the current approaches adopted by public youth policies in Spain and limitations and difficulties encountered by the government in attempting to meet the demands of young people; (3) social work with young people and professionals involved in youth policies. In the last section, we conclude with some open questions and proposals for the immediate future

Observation of Pulsed γ-Rays Above 25 GeV from the Crab Pulsar with MAGIC

One fundamental question about pulsars concerns the mechanism of their pulsed electromagnetic emission. Measuring the high-end region of a pulsar's spectrum would shed light on this question. By developing a new electronic trigger, we lowered the threshold of the Major Atmospheric γ-ray Imaging Cherenkov (MAGIC) telescope to 25 giga-electron volts. In this configuration, we detected pulsed γ-rays from the Crab pulsar that were greater than 25 giga-electron volts, revealing a relatively high cutoff energy in the phase-averaged spectrum. This indicates that the emission occurs far out in the magnetosphere, hence excluding the polar-cap scenario as a possible explanation of our measurement. The high cutoff energy also challenges the slot-gap scenario.

Improving the performance of the single-dish Cherenkov telescope MAGIC through the use of signal timing

The Cherenkov light flashes produced by Extensive Air Showers are very short in time. A high bandwidth and fast digitizing readout, therefore, can minimize the influence of the background from the light of the night sky, and improve the performance in Cherenkov telescopes. The time structure of the Cherenkov image can further be used in single-dish Cherenkov telescopes as an additional parameter to reduce the background from unwanted hadronic showers. A description of an analysis method which makes use of the time information and the subsequent improvement on the performance of the MAGIC telescope (especially after the upgrade with an ultra fast 2 GSamples/s digitization system in February 2007) will be presented. The use of timing information in the analysis of the new MAGIC data reduces the background by a factor two, which in turn results in an enhancement of about a factor 1.4 of the flux sensitivity to point-like sources, as tested on observations of the Crab Nebula.

Probing quantum gravity using photons from a flare of the active galactic nucleus Markarian 501 observed by the MAGIC telescope

We analyze the timing of photons observed by the MAGIC telescope during a flare of the active galactic nucleus Mkn 501 for a possible correlation with energy, as suggested by some models of quantum gravity (QG), which predict a vacuum refractive index similar or equal to 1 + (E/M-QGn)(n), n = 1, 2. Parametrizing the delay between gamma-rays of different energies as Delta t = +/-tau E-1 or Delta t = +/-tau E-q(2), we find tau(1) = (0.030 +/- 0.012) s/GeV at the 2.5-sigma level, and tau(q) = (3.71 +/- 2.57) x 10(-6) s/GeV2, respectively. We use these results to establish lower limits M-QG1 > 0.21 X 10(18) GeV and M-QG2 > 0.26 x 10(11) GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC sensitivity to propagation effects at these levels. Thermal plasma effects in the source are negligible, but we cannot exclude the importance of some other source effect.