Coexistence between fluid and crystalline phases of proteins in photosynthetic membranes

Photosystem II (PSII) and its associated light-harvesting complex II (LHCII) are highly concentrated in the stacked grana regions of photosynthetic thylakoid membranes. Within the membrane, PSII-LHCII supercomplexes can be arranged in disordered packings, ordered arrays, or mixtures thereof. The physical driving forces underlying array formation are unknown, complicating attempts to determine a possible functional role for arrays in regulating light harvesting or energy conversion efficiency. Here we introduce a coarse-grained model of protein interactions in coupled photosynthetic membranes, focusing on just two particle types that feature simple shapes and potential energies motivated by structural studies. Reporting on computer simulations of the model's equilibrium fluctuations, we demonstrate its success in reproducing diverse structural features observed in experiments, including extended PSII-LHCII arrays. Free energy calculations reveal that the appearance of arrays marks a phase transition from the disordered fluid state to a system-spanning crystal, which can easily be arrested by thermodynamic constraints or slow dynamics. The region of fluid-crystal coexistence is broad, encompassing much of the physiologically relevant parameter regime. Our results suggest that grana membranes lie at or near phase coexistence, conferring significant structural and functional flexibility to this densely packed membrane protein system.Comment: 11 pages, 5 figure

Momentum flux density, kinetic energy density and their fluctuations for one-dimensional confined gases of non-interacting fermions

We present a Green's function method for the evaluation of the particle density profile and of the higher moments of the one-body density matrix in a mesoscopic system of N Fermi particles moving independently in a linear potential. The usefulness of the method is illustrated by applications to a Fermi gas confined in a harmonic potential well, for which we evaluate the momentum flux and kinetic energy densities as well as their quantal mean-square fluctuations. We also study some properties of the kinetic energy functional E_{kin}[n(x)] in the same system. Whereas a local approximation to the kinetic energy density yields a multi-valued function, an exact single-valued relationship between the density derivative of E_{kin}[n(x)] and the particle density n(x) is demonstrated and evaluated for various values of the number of particles in the system.Comment: 10 pages, 5 figure

Caractérisation variétale de cépages musqués à raisin coloré au moyen de paramètres ampélographiques descriptifs et biochimiques

Vingt-deux cépages à saveur musquée à baie colorée cultivés dans une collection au Piédmont (Nord Quest d'Italie) ont été étudiés d'un point de vue ampélographique et biochimique. Des observations descriptives ont été effectuées sur les souches ainsi que l'analyse des terpénols libres et glycosylés du jus et des polyphénols de la pellicule des baies à maturité. Les données analytiques et ampélographiques ont été soumises à l'analyse statistique multidimensionelle (analyse des clusters et analyse des composantes principales).Les résultats obtenus ont permis de bien caractériser les 22 cépages examinés. Les observations déscriptives ont indiqué que certains cépages pouvaient être groupés selon leur profil morphologique (groupes de "Muscat à petits grains", de "Hambourg", etc.). L'analyse quali-quantitative des anthocyanidols et des esters hydroxycinnamoyltartriques du raisin a permis de former des groupes de cépages, différents aussi pour la couleur de la baie qui allait du rose clair, au rose foncé, au rouge, au violet et au bleunoir. De rélations entre des poliphenols de la pellicule et des composés terpeniques du jus, en plus, ont été mise en évidence: onl a observé par example que les raisins ou la cyanidine monoglucoside était l'anthocyanidol prédominant (couleur de la baie rose très claire) avaient le jus le plus riche en linalol.Morphological and biochemical characterisation of coloured berry-muscat grapevine cultivarsTwenty-two grapevine cultivars with muscat flavour and coloured berries grown in a collection vineyard in Piedmont (Northwest Italy) have been investigated by ampelographic and biochemical methods. Morphological and ampelographic observations have been carried out on the vines. Free and bound terpenes of the juice and berry skin phenolic compounds at maturity have also been analysed. The data were processed by multivariate statistical procedures (cluster and principal component analysis). The results allowed the successful characterisation of the cultivars. The ampelographic descriptive observations indicated that the cultivars could be grouped according to their morphological characteristics, viz. as similar to ''Muscat a petits grains'' or similar to ''Muscat of Hamburg'' etc.). Furthermore, the determination of berry skin anthocyanins together with hydroxycinnamoyl tartaric acids allowed to group according to the berry skin colour which varied from light rose to dark rose, red, violet and blue-black. Some juice terpenes showed relationships with some berry polyphenols: the cultivars richest in cyanidin (skin of light pink colour) were also the richest in linalool

The Pittsburgh Sloan Digital Sky Survey MgII Quasar Absorption-Line Survey Catalog

We present a catalog of intervening MgII quasar absorption-line systems in the redshift interval 0.36 <= z <= 2.28. The catalog was built from Sloan Digital Sky Survey Data Release Four (SDSS DR4) quasar spectra. Currently, the catalog contains > 17,000 measured MgII doublets. We also present data on the ~44,600 quasar spectra which were searched to construct the catalog, including redshift and magnitude information, continuum-normalized spectra, and corresponding arrays of redshift-dependent minimum rest equivalent widths detectable at our confidence threshold. The catalog is available on the web. A careful second search of 500 random spectra indicated that, for every 100 spectra searched, approximately one significant MgII system was accidentally rejected. Current plans to expand the catalog beyond DR4 quasars are discussed. Many MgII absorbers are known to be associated with galaxies. Therefore, the combination of large size and well understood statistics makes this catalog ideal for precision studies of the low-ionization and neutral gas regions associated with galaxies at low to moderate redshift. An analysis of the statistics of MgII absorbers using this catalog will be presented in a subsequent paper.Comment: AJ, in pres

Proximity-Induced Odd-Frequency Superconductivity in a Topological Insulator

At an interface between a topological insulator (TI) and a conventional superconductor (SC), superconductivity has been predicted to change dramatically and exhibit novel correlations. In particular, the induced superconductivity by an $s$-wave SC in a TI can develop an order parameter with a $p$-wave component. Here we present experimental evidence for an unexpected proximity-induced novel superconducting state in a thin layer of the prototypical TI, Bi$_2$Se$_3$, proximity coupled to Nb. From depth-resolved magnetic field measurements below the superconducting transition temperature of Nb, we observe a local enhancement of the magnetic field in Bi$_2$Se$_3$ that exceeds the externally applied field, thus supporting the existence of an intrinsic paramagnetic Meissner effect arising from an odd-frequency superconducting state. Our experimental results are complemented by theoretical calculations supporting the appearance of such a component at the interface which extends into the TI. This state is topologically distinct from the conventional Bardeen-Cooper-Schrieffer state it originates from. To the best of our knowledge, these findings present a first observation of bulk odd-frequency superconductivity in a TI. We thus reaffirm the potential of the TI-SC interface as a versatile platform to produce novel superconducting states.Comment: Accepted version for publication in Physical Review Letter

Quasiparticle Description of the QCD Plasma, Comparison with Lattice Results at Finite T and Mu

We compare our 2+1 flavor, staggered QCD lattice results with a quasiparticle picture. We determine the pressure, the energy density, the baryon density, the speed of sound and the thermal masses as a function of T and $\mu_B$. For the available thermodynamic quantities the difference is a few percent between the results of the two approaches. We also give the phase diagram on the $\mu_B$--T plane and estimate the critical chemical potential at vanishing temperature.Comment: 13 pages, 10 figure