Molecular Wires Acting as Coherent Quantum Ratchets

The effect of laser fields on the electron transport through a molecular wire being weakly coupled to two leads is investigated. The molecular wire acts as a coherent quantum ratchet if the molecule is composed of periodically arranged, asymmetric chemical groups. This setup presents a quantum rectifier with a finite dc-response in the absence of a static bias. The nonlinear current is evaluated in closed form within the Floquet basis of the isolated, driven wire. The current response reveals multiple current reversals together with a nonlinear dependence (reflecting avoided quasi-energy crossings) on both, the amplitude and the frequency of the laser field. The current saturates for long wires at a nonzero value, while it may change sign upon decreasing its length.Comment: 4 pages, 4 figures, RevTeX

Estudio comparativo del perfil de ácidos grasos de quesos de oveja comerciales

The present study was carried out to characterize the FA profile of sheep cheese marketed in Chile. Fifty-eight cheeses were collected from supermarkets of 5 different Chilean cities including 34 sheep cheeses, 7 from goat’s milk, 11 from cow’s milk, 4 from a mixture of sheep, goat and cow’s milk and 2 from a mixture of sheep and cow’s milk. Compared to the cow and goat cheese (3.4 and 2.5 g·100g−1), the sheep cheese (3.8 g·100g−1) contained higher contents of C18:1t. The saturated and polyunsatured FA contents were greater in goat cheese than in sheep and cow cheese. The n6/n3 ratio was greater in goat (6.1) cheese than in sheep and cow cheese (3.8 and 5.2). The atherogenicity index was unaffected by cheese type, however, the thrombogenic index was lower in sheep cheese (2.8) than in goat and cow cheese (3.1 and 2.9). The n6/n3 ratio and thrombogenic index were lower in Chilean sheep cheese than in those imported from Europe. The fatty acid profile of cheese can be used to differentiate animal species from which the cheese is made and to some extent the geographical origin that may give some insight as to animal feed and production management.Este estudio fue llevado a cabo para caracterizar el perfil de AG de quesos de oveja que se comercializan en Chile. Cincuenta y ocho quesos fueron recogidos de supermercados de 5 ciudades de Chile de los cuales 34 fueron de oveja, 7 de cabra, 11 de vaca, 4 de mezcla de leche de oveja, cabra y vaca y 2 de mezcla de leche de oveja y vaca. Comparado con quesos de vaca y cabra (3.4 y 2.5 g·100g−1), los quesos de oveja (3.8 g·100g−1) presentaron mayor contenido de C18:1t. Los AG saturados y poliinsaturados tuvieron concentraciones más altas en los quesos de cabra que en los quesos de oveja y vaca. La relación n6/n3 fue más alta en quesos de cabra (6.1) que en quesos de oveja y vaca (3.8 y 5.2). El índice aterogénico no fue afectado por el tipo de queso, sin embargo, el índice trombogénico fue menor en quesos de oveja (2.8) que en quesos de cabra y vaca (3.8 y 5.2). La relación n6/n3 y el índice trombogénico fueron menores en quesos chilenos que en quesos importados de Europa. El perfil de AG de quesos puede ser usado para diferenciar entre especies animales de las cuales proviene el queso y hasta cierto grado, el origen geográfico, ofreciendo indicios sobre el tipo de alimento y sistema productivo animal del cual provienen los quesos

Electron Standing Wave Formation in Atomic Wires

Using the Landauer formulation of transport theory and tight binding models of the electronic structure, we study electron transport through atomic wires that form 1D constrictions between pairs of metallic nano-contacts. Our results are interpreted in terms of electron standing waves formed in the atomic wires due to interference of electron waves reflected at the ends of the atomic constrictions. We explore the influence of the chemistry of the atomic wire-metal contact interfaces on these standing waves and the associated transport resonances by considering two types of atomic wires: gold wires attached to gold contacts and carbon wires attached to gold contacts. We find that the conductance of the gold wires is roughly $1 G_0 = 2 e^2/h$ for the wire lengths studied, in agreement with experiments. By contrast, for the carbon wires the conductance is found to oscillate strongly as the number of atoms in the wire varies, the odd numbered chains being more conductive than the even numbered ones, in agreement with previous theoretical work that was based on a different model of the carbon wire and metal contacts.Comment: 14 pages, includes 6 figure

Electron transport across a quantum wire in the presence of electron leakage to a substrate

We investigate electron transport through a mono-atomic wire which is tunnel coupled to two electrodes and also to the underlying substrate. The setup is modeled by a tight-binding Hamiltonian and can be realized with a scanning tunnel microscope (STM). The transmission of the wire is obtained from the corresponding Green's function. If the wire is scanned by the contacting STM tip, the conductance as a function of the tip position exhibits oscillations which may change significantly upon increasing the number of wire atoms. Our numerical studies reveal that the conductance depends strongly on whether or not the substrate electrons are localized. As a further ubiquitous feature, we observe the formation of charge oscillations.Comment: 7 pages, 7 figure

Hydrodynamic theory for granular gases

A granular gas subjected to a permanent injection of energy is described by means of hydrodynamic equations derived from a moment expansion method. The method uses as reference function not a Maxwellian distribution $f_{\sf M}$ but a distribution $f_0 = \Phi f_{\sf M}$, such that $\Phi$ adds a fourth cumulant $\kappa$ to the velocity distribution. The formalism is applied to a stationary conductive case showing that the theory fits extraordinarily well the results coming from our molecular dynamic simulations once we determine $\kappa$ as a function of the inelasticity of the particle-particle collisions. The shape of $\kappa$ is independent of the size $N$ of the system.Comment: 10 pages, 9 figures, more about our research in http://www.cec.uchile.cl/cinetica

Multiwavelength observations of 3C 454.3. III. Eighteen months of AGILE monitoring of the "Crazy Diamond"

We report on 18 months of multiwavelength observations of the blazar 3C 454.3 (Crazy Diamond) carried out in July 2007-January 2009. We show the results of the AGILE campaigns which took place on May-June 2008, July-August 2008, and October 2008-January 2009. During the May 2008-January 2009 period, the source average flux was highly variable, from an average gamma-ray flux F(E>100MeV) > 200E-8 ph/cm2/s in May-June 2008, to F(E>100MeV)~80E-8 ph/cm2/s in October 2008-January 2009. The average gamma-ray spectrum between 100 MeV and 1 GeV can be fit by a simple power law (Gamma_GRID ~ 2.0 to 2.2). Only 3-sigma upper limits can be derived in the 20-60 keV energy band with Super-AGILE. During July-August 2007 and May-June 2008, RXTE measured a flux of F(3-20 keV)= 8.4E-11 erg/cm2/s, and F(3-20 keV)=4.5E-11 erg/cm2/s, respectively and a constant photon index Gamma_PCA=1.65. Swift/XRT observations were carried out during all AGILE campaigns, obtaining a F(2-10 keV)=(0.9-7.5)E-11 erg/cm2/s and a photon index Gamma_XRT=1.33-2.04. BAT measured an average flux of ~5 mCrab. GASP-WEBT monitored 3C 454.3 during the whole 2007-2008 period from the radio to the optical. A correlation analysis between the optical and the gamma-ray fluxes shows a time lag of tau=-0.4 days. An analysis of 15 GHz and 43 GHz VLBI core radio flux observations shows an increasing trend of the core radio flux, anti- correlated with the higher frequency data. The modeling SEDs, and the behavior of the long-term light curves in different energy bands, allow us to compare the jet properties during different emission states, and to study the geometrical properties of the jet on a time-span longer than one year.Comment: Accepted for publication in ApJ. Adapted Abstract. 17 pages, 19 Figures, 5 Table

A new skilled emigration dynamic: Portuguese nurses and recruitment in the southern European periphery

Philippine and Indian nurses have been emigrating for many years, but Portu-guese nurses and other South and East Europeans have recently started to replace them in the UK. This study focuses on the recent migration of Portuguese nurses – both as emigrants and immigrants – within the European area. The research mixes extensive and intensive methodologies. Health agencies start-ed to recruit heavily among Portuguese nurses after 2008, which often led to their decision to leave the country with a guaranteed job abroad. In turn, this dynamic of emigration being motived by institutional and recruitment networks was caused by a structural factor: the barriers erected in 2010 by UK immigration pol-icies against the contracting of nurses from outside the EU, which led the job agencies to search for nurses inside Europe. The chapter’s main finding is that alt-hough the push factor of economic recession and increased unemployment that hit the European periphery after the 2008 financial crisis played a role in the out-flow of Portuguese nurses, it was the pull factor that was more significant. The second finding is that this new mass emigration of nurses is not just a Portuguese phenomenon but rather is in keeping with other Southern and East European pe-ripheral countries.info:eu-repo/semantics/publishedVersio