Some results on homoclinic and heteroclinic connections in planar systems

Consider a family of planar systems depending on two parameters $(n,b)$ and having at most one limit cycle. Assume that the limit cycle disappears at some homoclinic (or heteroclinic) connection when $\Phi(n,b)=0.$ We present a method that allows to obtain a sequence of explicit algebraic lower and upper bounds for the bifurcation set ${\Phi(n,b)=0}.$ The method is applied to two quadratic families, one of them is the well-known Bogdanov-Takens system. One of the results that we obtain for this system is the bifurcation curve for small values of $n$, given by $b=\frac5 7 n^{1/2}+{72/2401}n- {30024/45294865}n^{3/2}- {2352961656/11108339166925} n^2+O(n^{5/2})$. We obtain the new three terms from purely algebraic calculations, without evaluating Melnikov functions

Extension of charge-state-distribution calculations for ion-solid collisions towards low velocities and many-electron ions

Knowledge of the detailed evolution of the whole charge-state distribution of projectile ions colliding with targets is required in several fields of research such as material science and atomic and nuclear physics but also in accelerator physics, and in particular in regard to the several foreseen large-scale facilities. However, there is a lack of data for collisions in the nonperturbative energy domain and that involve many-electron projectiles. Starting from the etacha model we developed [Rozet, Nucl. Instrum. Methods Phys. Res., Sect. B 107, 67 (1996)10.1016/0168-583X(95)00800-4], we present an extension of its validity domain towards lower velocities and larger distortions. Moreover, the system of rate equations is able to take into account ions with up to 60 orbital states of electrons. The computed data from the different new versions of the etacha code are compared to some test collision systems. The improvements made are clearly illustrated by 28.9MeVu-1Pb56+ ions, and laser-generated carbon ion beams of 0.045 to 0.5MeVu-1, passing through carbon or aluminum targets, respectively. Hence, those new developments can efficiently sustain the experimental programs that are currently in progress on the "next-generation" accelerators or laser facilities.Fil: Lamour, E.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Fainstein, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Galassi, Mariel Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Prigent, C.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Ramirez, C. A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rivarola, Roberto Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rozet, J. P.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Trassinelli, M.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Vernhet, D.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; Franci

Modulating the phase transition temperature of giant magnetocaloric thin films by ion irradiation

Magnetic refrigeration based on the magnetocaloric effect at room temperature is one of the most attractive alternative to the current gas compression/expansion method routinely employed. Nevertheless, in giant magnetocaloric materials, optimal refrigeration is restricted to the narrow temperature window of the phase transition (Tc). In this work, we present the possibility of varying this transition temperature into a same giant magnetocaloric material by ion irradiation. We demonstrate that the transition temperature of iron rhodium thin films can be tuned by the bombardment of ions of Ne 5+ with varying fluences up to 10 14 ions cm --2 , leading to optimal refrigeration over a large 270--380 K temperature window. The Tc modification is found to be due to the ion-induced disorder and to the density of new point-like defects. The variation of the phase transition temperature with the number of incident ions opens new perspectives in the conception of devices using giant magnetocaloric materials

Electron gas polarization effect induced by heavy H-like ions of moderate velocities channeled in a silicon crystal

We report on the observation of a strong perturbation of the electron gas induced by 20 MeV/u U$^{91+}$ ions and 13 MeV/u Pb$^{81+}$ ions channeled in silicon crystals. This collective response (wake effect) in-duces a shift of the continuum energy level by more than 100 eV, which is observed by means of Radiative Electron Capture into the K and L-shells of the projectiles. We also observe an increase of the REC probability by 20-50% relative to the probability in a non-perturbed electron gas. The energy shift is in agreement with calculations using the linear response theory, whereas the local electron density enhancement is much smaller than predicted by the same model. This shows that, for the small values of the adiabaticity parameter achieved in our experiments, the density fluctuations are not strongly localized at the vicinity of the heavy ions

Electronic temperatures, densities and plasma X-ray emission of a 14.5 GHz Electron-Cyclotron Resonance Ion Source

We have performed a systematic study of the Bremsstrahlung emission from the electrons in the plasma of a commercial 14.5 GHz Electron-Cyclotron Resonance Ion Source. The electronic spectral temperature and the product of ionic and electronic densities of the plasma are measured by analyzing the Bremsstrahlung spectra recorded for several rare gases (Ar, Kr, Xe) as a function of the injected power. Within our uncertainty, we find an average temperature of ? 48 keV above 100W, with a weak dependency on the injected power and gas composition. Charge state distributions of extracted ion beams have been determined as well, providing a way to disentangle the ionic density from the electronic density. Moreover X-ray emission from highly charged argon ions in the plasma has been observed with a high-resolution mosaic crystal spectrometer, demonstrating the feasibility for high-precision measurements of transition energies of highly charged ions, in particular of the magnetic dipole (M1) transition of He-like of argon ions

State selective measurements of HCI produced by strong ultrashort laser clusters interaction

International audienceWe have performed studies of keV x-ray production from (Ar)n , (Kr)n and (Xe)n rare gas clusters (with n between 104 and 106 atoms/cluster) submitted to intense (~10^18 W/cm2) infrared (790 nm) laser pulses. We have determined the photon energies and the absolute photon emission yields as a function of several physical parameters governing the interaction : size and atomic number of the clusters, peak intensity of the laser. Up to 10^6 3 keV photons per pulse at a moderate (10^15/cm3) atomic density have been observed. High resolution spectroscopy studies in the case of (Ar)n clusters have also been performed, giving unambiguous evidence of highly charged (up to heliumlike) ions with K vacancies production. The results obtained indicate that X-rays are emitted before cluster explosion on a subpicosecond time scale, and shed some light on the mechanisms involved in the first stage of the production of the nanoplasma induced from each cluster

Dynamique sub-picoseconde de l'interaction laser de puissance – agrégats de gaz rare : émission intense de rayons X et production d'ions multichargés.

National audienceLors de campagnes d'expériences réalisées sur le Laser Ultra Court Accordable du CEA/Saclay, nous avons étudié le rayonnement X, tant qualitativement (spectroscopie et énergie moyenne des photons) que quantitativement (taux absolus et lois d'évolution), émis lors de l'interaction d'un jet effusif d'agrégats de gaz rare (Ar, Kr, Xe comprenant entre 10^4 et 10^6 atomes/agrégat) avec un laser femtoseconde de puissance (éclairement jusqu'à quelques 10^17 W/cm2). Les résultats présentés dans ce manuscrit sont uniquement dédiés aux agrégats d'Ar pour lesquels nous avons observé un rayonnement X issu d'ions fortement multichargés (jusqu'à l'Ar16+) présentant des lacunes en couches K. La technique de spectroscopie X utilisée a permis de déterminer pour la première fois des taux absolus ainsi que les lois d'évolution de l'émission X en fonction de l'ensemble des paramètres gouvernant l'interaction (intensité, polarisation, longueur d'onde et durée du pulse laser aussi bien que taille, densité et numéro atomique des agrégats)

The Photoreceptor Cell-Specific Nuclear Receptor Gene (PNR ) Accounts for Retinitis Pigmentosa in the Crypto-Jews from Portugal (Marranos), Survivors from the Spanish Inquisition

The last Crypto-Jews (Marranos) are the survivors of Spanish Jews who were persecuted in the late fifteenth century, escaped to Portugal and were forced to convert to save their lives. Isolated groups still exist in mountainous areas such as Belmonte in the Beira-Baixa province of Portugal. We report here the genetic study of a highly consanguineous endogamic population of Crypto-Jews of Belmonte affected with autosomal recessive retinitis pigmentosa (RP). A genome-wide search for homozygosity allowed us to localize the disease gene to chromosome 15q22-q24 (Zmax=2.95 at θ=0 at the D15S131 locus). Interestingly, the photoreceptor cell-specific nuclear receptor (PNR) gene, the expression of which is restricted to the outer nuclear layer of retinal photoreceptor cells, was found to map to the YAC contig encompassing the disease locus. A search for mutations allowed us to ascribe the RP of Crypto-Jews of Belmonte to a homozygous missense mutation in the PNR gene. Preliminary haplotype studies support the view that this mutation is relatively ancient but probably occurred after the population settled in Belmonte