Solidification of small para-H2 clusters at zero temperature

We have determined the ground-state energies of para-H$_2$ clusters at zero temperature using the diffusion Monte Carlo method. The liquid or solid character of each cluster is investigated by restricting the phase through the use of proper importance sampling. Our results show inhomogeneous crystallization of clusters, with alternating behavior between liquid and solid phases up to N=55. From there on, all clusters are solid. The ground-state energies in the range N=13--75 are established and the stable phase of each cluster is determined. In spite of the small differences observed between the energy of liquid and solid clusters, the corresponding density profiles are significantly different, feature that can help to solve ambiguities in the determination of the specific phase of H$_2$ clusters.Comment: 17 pages, accepted for publication in J. Phys. Chem.

Ca impurity in small mixed 4^4He-3^3He clusters

The structure of small mixed helium clusters doped with one calcium atom has been determined within the diffusion Monte Carlo framework. The results show that the calcium atom sits at the $^4$He-$^3$He interface. This is in agreement with previous studies, both experimental and theoretical, performed for large clusters. A comparison between the results obtained for the largest cluster we have considered for each isotope shows a clear tendency of the Ca atom to reside in a deep dimple at the surface of the cluster for $^4$He clusters, and to become fully solvated for $^3$He clusters. We have calculated the absorption spectrum of Ca around the $4s4p \leftarrow 4s^2$ transition and have found that it is blue-shifted from that of the free-atom transition by an amount that depends on the size and composition of the cluster.Comment: 24 pages, 11 figures. Accepted on Journal of Chemical Physic

Microscopic study of the He2-SF6 trimers

The He2-SF6 trimers, in their different He isotopic combinations, are studied both in the framework of the correlated Jastrow approach and of the Correlated Hyperspherical Harmonics expansion method. The energetics and structure of the He-SF6 dimers are analyzed, and the existence of a characteristic rotational band in the excitation spectrum is discussed, as well as the isotopic differences. The binding energies and the spatial properties of the trimers, in their ground and lowest lying excited states, obtained by the Jastrow ansatz are in excellent agreement with the results of the converged CHH expansion. The introduction of the He-He correlation makes all trimers bound by largely suppressing the short range He-He repulsion. The structural properties of the trimers are qualitatively explained in terms of the shape of the interactions, Pauli principle and masses of the constituents.Comment: 17 pages, 5 figures. Submitted to PR

Silicon-based three-dimensional microstructures for radiation dosimetry in hadrontherapy

In this work, we propose a solid-state-detector for use in radiation microdosimetry. This device improves the performance of existing dosimeters using customized 3D-cylindrical microstructures etched inside silicon. The microdosimeter consists of an array of micro-sensors that have 3D-cylindrical electrodes of 15 μm diameter and a depth of 5 μm within a silicon membrane, resulting in a well-defined micrometric radiation sensitive volume. These microdetectors have been characterized using an 241Am source to assess their performance as radiation detectors in a high-LET environment. This letter demonstrates the capability of this microdetector to be used to measure dose and LET in hadrontherapy centers for treatment plan verification as part of their patient-specific quality control program

Ground state properties of a dilute homogeneous Bose gas of hard disks in two dimensions

The energy and structure of a dilute hard-disks Bose gas are studied in the framework of a variational many-body approach based on a Jastrow correlated ground state wave function. The asymptotic behaviors of the radial distribution function and the one-body density matrix are analyzed after solving the Euler equation obtained by a free minimization of the hypernetted chain energy functional. Our results show important deviations from those of the available low density expansions, already at gas parameter values $x\sim 0.001$. The condensate fraction in 2D is also computed and found generally lower than the 3D one at the same $x$.Comment: Submitted to PRA. 7 pages and 8 figure

State-dependent Jastrow correlation functions for 4He nuclei

We calculate the ground-state energy for the nucleus 4He with V4 nucleon interactions, making use of a Jastrow description of the corresponding wavefunction with state-dependent correlation factors. The effect related to the state dependence of the correlation is quite important, lowering the upper bound for the ground-state energy by some 2 MeV.Comment: 10 pages, REVTeX, to be published in J. Phys. G: Nucl. Part. Phy

Primula hirsuta All. dans les Pyrénées orientales

Confirmem la presència d’aquesta espècie als Pirineus Orientals basant-nos en noves recol•leccions i observacions de camp. A més a més, presentem una revisió crítica de les citacions anteriors i dels testimonis d’herbari existents. Finalment, resumim la corologia d’aquesta espècie als Pirineus i concloem que hauria d’ésser considerada com a vulnerable (VU) a Catalunya seguint els criteris de l’UICN.Our new collections and field observations confirm the presence of this species in the Eastern Pyrenees. Moreover, we present a critical revision of the previous doubtful citations and of the extant herbarium sheets. Finally, we sum up the chorology of the species on the Pyrenean range and we conclude that the species should be considered as vulnerable (VU) in Catalonia according to criteria UICN.Nos nouvelles récoltes et données de terrain confirment la présence de cette espèce dans la partie orientale des Pyrénées, mise en doute dans quelques travaux ibériques récents. Aussi, nous présentons une révision critique des citations antérieures et des échantillons d’herbier existants. Nous résumons la chorologie de cette espèce dans les Pyrénées et concluons au final que le statut de conservation de ce taxon en Catalogne est vulnérable (VU) selon les critères de l’UICN

ECU-oriented models for NOx prediction. Part 2: adaptive estimation by using an NOx sensor

The implantation of nitrogen oxide sensors in diesel engines is necessary in order to track emissions at the engine exhaust line for diagnosis and control of the after-treatment devices. However, the use of models is still necessary since the sensor outputs are delayed and filtered. The present paper deals with the problem of the nitrogen oxide estimation in two parts; Part 1 deals with a control-oriented model for the nitrogen oxide estimation, while Part 2 presents data fusion of the model and the sensor to improve the estimation, which is presented in the following. The use of models for the nitrogen oxide estimation is an alternative but the drift and the ageing are still issues. In order to overcome this problem, the fusion of different signals can be carried out in a smart way by means of a Kalman filter. There exist different ways of presenting this fusion, from directly tracking the bias to updating the model parameters. For this, different algorithms are proposed in this paper with the aim of correcting the model output. Furthermore, the estimation of the actual nitrogen oxide concentration, by preventing sensor delay and filtering, is also integrated in the algorithm, which is a suitable strategy for combining nitrogen oxide sensors and models on an onboard basis.Guardiola, C.; Climent, H.; Pla Moreno, B.; Blanco-Rodriguez, D. (2015). ECU-oriented models for NOx prediction. Part 2: adaptive estimation by using an NOx sensor. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. 229(10):1345-1360. doi:10.1177/0954407014561278S134513602291

A family of complex potentials with real spectrum

We consider a two-parameter non hermitean quantum-mechanical hamiltonian that is invariant under the combined effects of parity and time reversal transformation. Numerical investigation shows that for some values of the potential parameters the hamiltonian operator supports real eigenvalues and localized eigenfunctions. In contrast with other PT symmetric models, which require special integration paths in the complex plane, our model is integrable along a line parallel to the real axis.Comment: Six figures and four table