Dynamics of molecular nanomagnets in time-dependent external magnetic fields: Beyond the Landau-Zener-St\"{u}ckelberg model

The time evolution of the magnetization of a magnetic molecular crystal is obtained in an external time-dependent magnetic field, with sweep rates in the kT/s range. We present the 'exact numerical' solution of the time dependent Schr\"{o}dinger equation, and show that the steps in the hysteresis curve can be described as a sequence of two-level transitions between adiabatic states. The multilevel nature of the problem causes the transition probabilities to deviate significantly from the predictions of the Landau-Zener-St\"{u}ckelberg model. These calculations allow the introduction of an efficient approximation method that accurately reproduces the exact results. When including phase relaxation by means of an appropriate master equation, we observe an interplay between coherent dynamics and decoherence. This decreases the size of the magnetization steps at the transitions, but does not modify qualitatively the physical picture obtained without relaxation.Comment: 8 pages, 7 figure

Tunable quantum dots in bilayer graphene

We demonstrate theoretically that quantum dots in bilayers of graphene can be realized. A position-dependent doping breaks the equivalence between the upper and lower layer and lifts the degeneracy of the positive and negative momentum states of the dot. Numerical results show the simultaneous presence of electron and hole confined states for certain doping profiles and a remarkable angular momentum dependence of the quantum dot spectrum which is in sharp contrast with that for conventional semiconductor quantum dots. We predict that the optical spectrum will consist of a series of non-equidistant peaks.Comment: 5 pages, to appear in Nano Letter

Landau levels and oscillator strength in a biased bilayer of graphene

We obtain analytical expressions for the eigenstates and the Landau level spectrum of biased graphene bilayers in a magnetic field. The calculations are performed in the context of a four-band continuum model and generalize previous approximate results. Solutions are presented for the spectrum as a function of interlayer coupling, the potential difference between the layers and the magnetic field. The explicit expressions allow us to calculate the oscillator strength and the selection rules for electric dipole transitions between the Landau states. Some transitions are significantly shifted in energy relative to those in an unbiased bialyer and exhibit a very different magnetic field dependence.Comment: To appear in Phys. Rev.

Snake states in graphene quantum dots in the presence of a p-n junction

We investigate the magnetic interface states of graphene quantum dots that contain p-n junctions. Within a tight-binding approach, we consider rectangular quantum dots in the presence of a perpendicular magnetic field containing p-n, as well as p-n-p and n-p-n junctions. The results show the interplay between the edge states associated with the zigzag terminations of the sample and the snake states that arise at the p-n junction, due to the overlap between electron and hole states at the potential interface. Remarkable localized states are found at the crossing of the p-n junction with the zigzag edge having a dumb-bell shaped electron distribution. The results are presented as function of the junction parameters and the applied magnetic flux.Comment: 13 pages, 23 figures, to be appeared in Phys. Rev.

Confined states and direction-dependent transmission in graphene quantum wells

We report the existence of confined massless fermion states in a graphene quantum well (QW) by means of analytical and numerical calculations. These states show an unusual quasi-linear dependence on the momentum parallel to the QW: their number depends on the wavevector and is constrained by electron-hole conversion in the barrier regions. An essential difference with non-relativistic electron states is a mixing between free and confined states at the edges of the free-particle continua, demonstrated by the direction-dependent resonant transmission across a potential well.Comment: Submitted to PR

BioRePortAP, an electronic clinical record coupled with a database : an example of its use in a single

Aims: To evaluate the efficacy and safety of the treatment of psoriatic arthritis (PsA) patients with tumor necrosis factor (TNF) antagonists in the Rheumatology Department of Hospital de Santa Maria using the BioRePortAP. Methods: The Portuguese Society of Rheumatology (SPR) developed an electronic medical chart coupled with a database for the follow up of PsA patients, the BioRePortAP, which was launched in May 2009. This evaluation was based on all the PsA patients that were on active treatment with TNF antagonists in September 2009 and were registered in the BioRePortAP. All the previous data on these patients were introduced in BioRePortAP using the prospective paper based follow up protocol that this Department was using since 1999. Only patients with more than 9 months of treatment were analyzed. Results: Forty-two patients with PsA, actively treated with anti-TNF agents in September 2009, for at least 9 months, were analyzed in BioRePortAP. Twenty-three patients were male (55%) and nineteen were female (45%). The average age of these patients was 49.8±10.9 years old, the average disease duration was of 10.7±5.6 years and the mean duration of biological therapy was of 37.8±27.8 months. For the 81% of patients with peripheral joint disease there was a mean reduction of more than 80% in the swollen and tender joint counts, and almost 50% in the health assessment questionnaire (HAQ) value. In the 19% of the patients with axial involvement the reduction of BASDAI and BASFI was not statistically significative. On top of that, PASI score suffered a reduction of 64%. Fourteen patients (33.3%) had to switch their TNF antagonist treatment. 58.8% of the switches were due to adverse effects and 41.2% due to therapy failure. Regarding the 56 adverse reactions registered, only one was a severe reaction. The remaining adverse reactions were not severe and 67% of them were due to infections. Discussion: The results of this first report of the use of the BioRePortAP in clinical practice confirm the efficacy and safety of TNF antagonist treatment in PsA. The results shown here elucidate the potential applications of BioRePortAP as a tool for efficacy and safety assessment of PsA patients treated with biotechnological drugs

Topological confinement in graphene bilayer quantum rings

We demonstrate the existence of localized electron and hole states in a ring-shaped potential kink in biased bilayer graphene. Within the continuum description, we show that for sharp potential steps the Dirac equation describing carrier states close to the K (or K') point of the first Brillouin zone can be solved analytically for a circular kink/anti-kink dot. The solutions exhibit interfacial states which exhibit Aharonov-Bohm oscillations as functions of the height of the potential step and/or the radius of the ring