Infinite average lifetime of an unstable bright state in the green fluorescent protein

The time evolution of the fluorescence intensity emitted by well-defined ensembles of Green Fluorescent Proteins has been studied by using a standard confocal microscope. In contrast with previous results obtained in single molecule experiments, the photo-bleaching of the ensemble is well described by a model based on Levy statistics. Moreover, this simple theoretical model allows us to obtain information about the energy-scales involved in the aging process.Comment: 4 pages, 4 figure

Magnetic-Island Contraction and Particle Acceleration in Simulated Eruptive Solar Flares

The mechanism that accelerates particles to the energies required to produce the observed high-energy impulsive emission in solar flares is not well understood. Drake et al. (2006) proposed a mechanism for accelerating electrons in contracting magnetic islands formed by kinetic reconnection in multi-layered current sheets. We apply these ideas to sunward-moving flux ropes (2.5D magnetic islands) formed during fast reconnection in a simulated eruptive flare. A simple analytic model is used to calculate the energy gain of particles orbiting the field lines of the contracting magnetic islands in our ultrahigh-resolution 2.5D numerical simulation. We find that the estimated energy gains in a single island range up to a factor of five. This is higher than that found by Drake et al. for islands in the terrestrial magnetosphere and at the heliopause, due to strong plasma compression that occurs at the flare current sheet. In order to increase their energy by two orders of magnitude and plausibly account for the observed high-energy flare emission, the electrons must visit multiple contracting islands. This mechanism should produce sporadic emission because island formation is intermittent. Moreover, a large number of particles could be accelerated in each magnetohydrodynamic-scale island, which may explain the inferred rates of energetic-electron production in flares. We conclude that island contraction in the flare current sheet is a promising candidate for electron acceleration in solar eruptions.Comment: Accepted for publication in The Astrophysical Journal (2016

Large 2D Coulomb crystals in a radio frequency surface ion trap

We designed and operated a surface ion trap, with an ion-substrate distance of 500\mum, realized with standard printed-circuit-board techniques. The trap has been loaded with up to a few thousand Sr+ ions in the Coulomb-crystal regime. An analytical model of the pseudo-potential allowed us to determine the parameters that drive the trap into anisotropic regimes in which we obtain large (N>150) purely 2D ion Coulomb crystals. These crystals may open a simple and reliable way to experiments on quantum simulations of large 2D systems.Comment: 4 pages, 4 figure

XAD2 resin in separation of phenolics

La résine XAD2 dans la séparation des composés phénoliquesOn a séparé les acides hydroxy cinnamyl tartriques, les acides phénoliques libres, les catéchines, les proanthocyanidines et les pigments libres et polymérisés du vin par adsorption sur la résine XAD2 suivie par l'élution avec des solvents organiques inertes. Les fractions ainsi obtenues sont analysées par CLHP

Berry Size and Qualitative Characteristics of Vitis vinifera L. cv. Syrah

The effect of variation in berry size on berry composition was studied in irrigated Syrah/R99 grapevines,located in a temperate area of South Africa. Berries from 45 clusters, sampled from both sides of the canopy(east and west), were weighed to create four categories: 1. less or equal to 1.5 g; 2. between 1.51 g and 2.00 g;3. between 2.01 g and 2.50 g; 4. more than 2.50 g. Berry physical characteristics were determined and totalanthocyanins and seed flavonoids were analysed by spectrophotometry and anthocyanin profiles by HPLC. Theratio of skin weight:berry weight did not change with increasing berry size, but the ratio of seed weight:berryweight increased. For total anthocyanins, varying results were obtained if values were expressed in mg/berry,mg/g skin, mg/kg grape and mg/cm2 skin. The quantity of total anthocyanins changed positively with increasingberry weight if expressed in mg/berry and remained almost similar if expressed in mg/cm2 of skin. In contrast,total polyphenols decreased with berry weight if the values were expressed in mg/kg grape and in mg/g skin.Total anthocyanins expressed in mg/kg grape and in mg/g skin were correlated positively to the number ofberries as well as to the total skin surface in one kilogram of grape. In this study, the largest berries seemed tohave lower quality characteristics. In order to obtain better wine quality, it seems important to reduce berryweight and, in general, berry size variability of Syrah. The obtainment and continuity of a particular wine stylemay be affected by berry variability

Plant Diversity in an Intensively Cultivated Vineyard Agroecosystem (Langhe, North-West Italy)

In areas of intensive agriculture, wild plant species are confined to field margins, thus they play a role inprotecting biodiversity. The aim of the present study was to assess plant diversity in an area of intensiveviticulture and to evaluate, for the first time, the impact of field margins on vineyard flora biodiversity. Thestudy was conducted in North-West Italy, were five categories of floristic lists in vineyard-margin pairs weresampled and compared. Five margins were identified: grass-covered (A) and bare (B) headlands, small (C)and wide (D) woodlands, and shrub and herbaceous (E) areas. Two hundred and fifty-two taxa were found,although only 19 were widespread. Differences among categories emerged, highlighting the high floristiccomplexity of the sites surrounded by wide wooded areas (D). The findings suggest an influence of marginsize, in addition to margin type, on the floristic richness of the vineyard. Moreover, an inverse relationshipbetween species richness and both the presence of Poaceae and the degree of soil grass coverage emerged.Enhancing biodiversity, at landscape and field level, by the appropriate management of cover crops andecological infrastructures, within and around vineyards, could be a strategy in sustainable viticulture.The increase in plant species richness is not an end in itself, but it might help to promote biodiversity atdifferent trophic levels

Topologically decoherence-protected qubits with trapped ions

We show that trapped ions can be used to simulate a highly symmetrical Hamiltonian with eingenstates naturally protected against local sources of decoherence. This Hamiltonian involves long range coupling between particles and provides a more efficient protection than nearest neighbor models discussed in previous works. Our results open the perspective of experimentally realizing in controlled atomic systems, complex entangled states with decoherence times up to nine orders of magnitude longer than isolated quantum systems.Comment: 4 page

Gas-dynamic shock heating of post-flare loops due to retraction following localized, impulsive reconnection

We present a novel model in which shortening of a magnetic flux tube following localized, three-dimensional reconnection generates strong gas-dynamic shocks around its apex. The shortening releases magnetic energy by progressing away from the reconnection site at the Alfven speed. This launches inward flows along the field lines whose collision creates a pair of gas-dynamic shocks. The shocks raise both the mass density and temperature inside the newly shortened flux tube. Reconnecting field lines whose initial directions differ by more that 100 degrees can produce a concentrated knot of plasma hotter that 20 MK, consistent with observations. In spite of these high temperatures, the shocks convert less than 10% of the liberated magnetic energy into heat - the rest remains as kinetic energy of bulk motion. These gas-dynamic shocks arise only when the reconnection is impulsive and localized in all three dimensions; they are distinct from the slow magnetosonic shocks of the Petschek steady-state reconnection model

Slow shocks and conduction fronts from Petschek reconnection of skewed magnetic fields: two-fluid effects

In models of fast magnetic reconnection, flux transfer occurs within a small portion of a current sheet triggering stored magnetic energy to be thermalized by shocks. When the initial current sheet separates magnetic fields which are not perfectly anti-parallel, i.e. they are skewed, magnetic energy is first converted to bulk kinetic energy and then thermalized in slow magnetosonic shocks. We show that the latter resemble parallel shocks or hydrodynamic shocks for all skew angles except those very near the anti-parallel limit. As for parallel shocks, the structures of reconnection-driven slow shocks are best studied using two-fluid equations in which ions and electrons have independent temperature. Time-dependent solutions of these equations can be used to predict and understand the shocks from reconnection of skewed magnetic fields. The results differ from those found using a single-fluid model such as magnetohydrodynamics. In the two-fluid model electrons are heated indirectly and thus carry a heat flux always well below the free-streaming limit. The viscous stress of the ions is, however, typically near the fluid-treatable limit. We find that for a wide range of skew angles and small plasma beta an electron conduction front extends ahead of the slow shock but remains within the outflow jet. In such cases conduction will play a more limited role in driving chromospheric evaporation than has been predicted based on single-fluid, anti-parallel models

Double-lambda microscopic model for entangled light generation by four-wave-mixing

Motivated by recent experiments, we study four-wave-mixing in an atomic double-{\Lambda} system driven by a far-detuned pump. Using the Heisenberg-Langevin formalism, and based on the microscopic properties of the medium, we calculate the classical and quantum properties of seed and conju- gate beams beyond the linear amplifier approximation. A continuous variable approach gives us access to relative-intensity noise spectra that can be directly compared to experiments. Restricting ourselves to the cold-atom regime, we predict the generation of quantum-correlated beams with a relative-intensity noise spectrum well below the standard quantum limit (down to -6 dB). Moreover entanglement between seed and conjugate beams measured by an inseparability down to 0.25 is expected. This work opens the way to the generation of entangled beams by four-wave mixing in a cold atomic sample.Comment: 11 pages, 6 figures, submitted to PR