Gate induced enhancement of spin-orbit coupling in dilute fluorinated graphene

We analyze the origin of spin-orbit coupling (SOC) in fluorinated graphene using Density Functional Theory (DFT) and a tight-binding model for the relevant orbitals. As it turns out, the dominant source of SOC is the atomic spin-orbit of fluorine adatoms and not the impurity induced SOC based on the distortion of the graphene plane as in hydrogenated graphene. More interestingly, our DFT calculations show that SOC is strongly affected by both the type and concentrations of the graphene's carriers, being enhanced by electron doping and reduced by hole doping. This effect is due to the charge transfer to the fluorine adatom and the consequent change in the fluorine-carbon bonding. Our simple tight-binding model, that includes the SOC of the $2p$ orbitals of F and effective parameters based on maximally localized Wannier functions, is able to account for the effect. The strong enhancement of the SOC induced by graphene doping opens the possibility to tune the spin relaxation in this material.Comment: 9 pages, 8 figure

Diffusion of fluorine adatoms on doped graphene

We calculate the diffusion barrier of fluorine adatoms on doped graphene in the diluted limit using Density Functional Theory. We found that the barrier $\Delta$ strongly depends on the magnitude and character of the graphene's doping ($\delta n$): it increases for hole doping ($\delta n<0$) and decreases for electron doping ($\delta n>0$). Near the neutrality point the functional dependence can be approximately by $\Delta=\Delta_0-\alpha\, \delta n$ where $\alpha\simeq6\times10^{-12}$ meVcm$^2$. This effect leads to significant changes of the diffusion constant with doping even at room temperature and could also affect the low temperature diffusion dynamics due to the presence of substrate induced charge puddles. In addition, this might open up the possibility to engineer the F dynamics on graphene by using local gates.Comment: 4 pages, 4 figure

Anomalous diffusion in the resonant quantum kicked rotor

We study the resonances of the quantum kicked rotor subjected to an excitation that follows a deterministic time-dependent prescription. For the primary resonances we find an analytical relation between the long-time behavior of the standard deviation and the external kick strength. For the secondary resonances we obtain essentially the same result numerically. Selecting the time sequence of the kick allows to obtain a variety of asymptotic wave-function spreadings: super-ballistic, ballistic, sub-ballistic, diffusive, sub-diffusive and localized.Comment: 5 pages, 3 figures To appear in Physica A

Artrópodos (Arthropoda: Arachnida e Insecta) asociados a los nidos de Neotoma mexicana (Mammalia: Rodentia) de San Miguel de Allende, Guanajuato, México

Los nidos de roedores son el refugio de distintas especies de artrópodos como pueden ser: ácaros, pulgas, chinches, piojos y pseudoescorpiones, entre otros. Algunos de ellos son de importancia médica y veterinaria porque son vectores de diversas enfermedades que pueden trasmitir al ser humano, animales domésticos y silvestres. Se recolectó un nido de Neotoma a partir del cual se identificaron 148 artrópodos de tres órdenes: Acari, Pseudoscorpiones (Arachnida) (Shultz, 2007) y Siphonaptera (Insecta). La especie más abundante fue el ácaro Cheyletus eruditus (Acari: Prostigmata: Cheyletidae) con 126 ejemplares. Tectocepheus velatus (Acari: Oribatida: Tectocepheidae) es un nuevo registro para los nidos de Neotoma. Los pseudoescorpiones representan el primer registro para Guanajuato, siendo Parachernes un nuevo registro para este microhábitat. Del orden Siphonaptera Tunga monositus es un nuevo registro para Guanajuato.The nests of rodents are the refuge of different species of arthropods such as mites, fleas, bugs, lice, and pseudoscorpions, among others. Some of them are of veterinary and medical importance because they are vectors of diverse diseases that can be transmitted to a human, domestic and wild animals. A nest of Neotoma mexicana was collected, from which 148 arthropods of four orders were found: Acari, Pseudoscorpiones (Arachnida), and Siphonaptera (Insecta). The most abundant species of mites was Cheyletus eruditus (Acari: Prostigmata: Chayletidae) with 126. Tectocepheus velatus (Acari: Oribatida: Tectocepheidae) is a new record for Neotoma nests. The pseudoscorpions represent the first records for Guanajuato, being Parachernes a new record for this microhabitat. Whilst for the order Siphonaptera Tunga monositus is a new record for Guanajuato

Valorization of Tomato Processing by-Products: Fatty Acid Extraction and Production of Bio-Based Materials

A method consisting of the alkaline hydrolysis of tomato pomace by-products has been optimized to obtain a mixture of unsaturated and polyhydroxylated fatty acids as well as a non-hydrolysable secondary residue. Reaction rates and the activation energy of the hydrolysis were calculated to reduce costs associated with chemicals and energy consumption. Lipid and non-hydrolysable fractions were chemically (infrared (IR) spectroscopy, gas chromatography/mass spectrometry (GC-MS)) and thermally (differential scanning calorimetry (DSC), thermogravimetric analysis (TGA)) characterized. In addition, the fatty acid mixture was used to produce cutin-based polyesters. Freestanding films were prepared by non-catalyzed melt-polycondensation and characterized by Attenuated Total Reflected-Fourier Transform Infrared (ATR-FTIR) spectroscopy, solid-state nuclear magnetic resonance (NMR), DSC, TGA, Water Contact Angles (WCA), and tensile tests. These bio-based polymers were hydrophobic, insoluble, infusible, and thermally stable, their physical properties being tunable by controlling the presence of unsaturated fatty acids and oxygen in the reaction. The participation of an oxidative crosslinking side reaction is proposed to be responsible for such modifications.Andalusian Regional Government P11-TEP-7418Spanish Ministerio de Economía y Competitividad AGL2015-65246-R and AGL2017-83036-RFondo Europeo de Desarrollo Regional (FEDER) AGL2015-65246-R and AGL2017-83036-

High resolution spectroscopy of the high velocity hot post-AGB star LS III +52 24 (IRAS 22023+5249)

The first high-resolution (R~50,000) optical spectrum of the B-type star, LS III +52 24, identified as the optical counterpart of the hot post-AGB candidate IRAS 22023+5249 (I22023) is presented. We report the detailed identifications of the observed absorption and emission features in the full wavelength range (4290-9015 A) as well as the atmospheric parameters and photospheric abundances (under the Local Thermodinamic Equilibrium approximation) for the first time. The nebular parameters (Te, Ne) are also derived. We estimate Teff=24,000 K, log g=3.0, xi=7 kms-1 and the derived abundances indicate a slightly metal-deficient evolved star with C/O<1. The observed P-Cygni profiles of hydrogen and helium clearly indicate on-going post-AGB mass loss. The presence of [N II] and [S II] lines and the non-detection of [O III] indicate that photoionisation has just started. The observed spectral features, large heliocentric radial velocity, atmospheric parameters, and chemical composition indicate that I22023 is an evolved post-AGB star belonging to the old disk population. The derived nebular parameters (Te=7000 K, Ne=1.2x104 cm-3) also suggest that I22023 may be evolving into a compact, young low-excitation Planetary Nebula. Our optical spectroscopic analysis together with the recent Spitzer detection of double-dust chemistry (the simultaneous presence of carbonaceous molecules and amorphous silicates) in I22023 and other B-type post-AGB candidates may point to a binary system with a dusty disk as the stellar origin common to the hot post-AGB stars with O-rich central stars.Comment: Accepted for publication in MNRAS (22 pages, 4 figures, and 8 tables). arXiv admin note: substantial text overlap with arXiv:0707.059