Tunneling induced electron transfer between separated protons

We study electron transfer between two separated nuclei using local control theory. By conditioning the algorithm in a symmetric system formed by two protons, one can favored slow transfer processes, where tunneling is the main mechanism, achieving transfer efficiencies close to unity assuming fixed nuclei. The solution can be parametrized using sequences of pump and dump pi pulses, where the pump pulse is used to excite the electron to a highly excited state where the time for tunneling to the target nuclei is on the order of femtoseconds. The time delay must be chosen to allow for full population transfer via tunneling, and the dump pulse is chosen to remove energy from the state to avoid tunneling back to the original proton. Finally, we study the effect of the nuclear kinetic energy on the transfer efficiency. Even in the absence of relative motion between the protons, the spreading of the nuclear wave function is enough to reduce the yield of electronic transfer to less than one half.Comment: 7 pages, 8 figure

Detrital zircon from a late Paleozoic accretionary complex of SW Iberia (Variscan Belt): History of crustal growth and recycling at the Rheic convergent margin

In this study we present new U-Pb ages of detrital zircons from greywackes and quartzites of the Pulo do Lobo Anticline (PLA) that have been interpreted to represent a Late Paleozoic accretionary complex in SW Iberia. The PLA separates the Ossa Morena Zone, which has a North- Gondwana affinity throughout Late Ediacaran and Early Paleozoic times, from the South Portuguese Zone, which is considered to be underlain by Laurussia basement. The PLA stratigraphy most likely represents a synorogenic basin that records the closure of the Late Paleozoic Rheic Ocean and the amalgamation of Pangaea. The youngest formations of the PLA contain upper Devonian microfossils.The results obtained indicate that the detrital zircons from the PLA represent a wide range of Precambrian and Paleozoic crystallization ages. Recycling of older sedimentary units of the Late Ediacaran active margin (Cadomian/Pan-African orogenies) as well as of the Early Paleozoic rifting and passive margin (Rheic Ocean) stages, accounts for the older populations with North-Gondwana affinity (Cambrian, Neoproterozoic, Paleoproterozoic and Archean, with a gap of Mesoproterozoic-age). However, the Mesoproterozoic detrital zircon ages found in the greywackes of the Pulo do Lobo Formation (< 7%) that do not correspond to any substantial source within North-Gondwana, could come from recycled sedimentary deposits or from denudation of Grenville-age basement (Laurussia?). The more recent formations present in the northern limb (Ferreira-Ficalho Group) of the PLA show a significant age cluster in the upper Devonian (c. 378 Ma), whereas on the southern limb (Chança Group), samples have from base to top of the stratigraphic sequence: a minor age cluster in the middle Devonian (c. 390 Ma), a significant age cluster in upper Devonian (c. 380 Ma) and very significant age cluster in the upper Devonian (c. 372 Ma). The presence of middle-upper Devonian detrital zircons in combination with very low abundances of Mesoproterozoic detrital zircon suggests that the PLA sedimentary rocks were not derived from exotic sources but rather have a North-Gondwanan origin. The zircon population in the interval c. 390-380 Ma has no identified corresponding magmatic or stratigraphic source in SW Iberia. Considering that, during the development of the upper Devonian basins of SW Iberia, Laurussia basement was not exposed and that there was no magmatic arc on the North-Gondwana margin, we suggest that the c. 390- 380 Ma detrital zircons are most probably derived from denudation of a (intra-oceanic) magmatic arc related to the closure of the Rheic Ocean

High-repetition-rate femtosecond laser processing of acrylic intra-ocular lenses

The study of laser processing of acrylic intra-ocular lenses (IOL) by using femtosecond laser pulses delivered at high-repetition rate is presented in this work. An ultra-compact air-cooled femtosecond diode laser (HighQ2-SHG, Spectra-Physics) delivering 250 fs laser pulses at the fixed wavelength of 520 nm with a repetition rate of 63 MHz was used to process the samples. Laser inscription of linear periodic patterns on the surface and inside the acrylic substrates was studied as a function of the processing parameters as well as the optical absorption characteristics of the sample. Scanning Electron Microscopy (SEM) Energy Dispersive X-ray Spectroscopy (EDX), and micro-Raman Spectroscopy were used to evaluate the compositional and microstructural changes induced by the laser radiation in the processed areas. Diractive characterization was used to assess 1st-order efficiency and the refractive index change

Control of bulk superconductivity in a BCS superconductor by surface charge doping via electrochemical gating

The electrochemical gating technique is a powerful tool to tune the surface conduction properties of various materials by means of pure charge doping, but its efficiency is thought to be hampered in materials with a good electronic screening. We show that, if applied to a metallic superconductor (NbN thin films), this approach allows observing reversible enhancements or suppressions of the bulk superconducting transition temperature, which vary with the thickness of the films. These results are interpreted in terms of proximity effect, and indicate that the effective screening length depends on the induced charge density, becoming much larger than that predicted by standard screening theory at very high electric fields