Bilayers of nucleosome core particles

Among the multiple effects involved in chromatin condensation and decondensation processes, interactions between nucleosome core particles are suspected to play a crucial role. We analyze them in the absence of linker DNA and added proteins, after the self-assembly of isolated nucleosome core particles under controlled ionic conditions. We describe an original lamellar mesophase forming tubules on the mesoscopic scale. High resolution imaging of cryosections of vitrified samples reveals how nucleosome core particles stack on top of one another into columns which themselves align to form bilayers that repel one another through a solvent layer. We deduce from this structural organization how the particles interact through attractive interactions between top and bottom faces and lateral polar interactions that originate in the heterogeneous charge distribution at the surface of the particle. These interactions, at work under conditions comparable with those found in the living cell, should be of importance in the mechanisms governing chromatin compaction in vivo

Ion-dependent dynamics of DNA ejections for bacteriophage lambda

We study the control parameters that govern the dynamics of in vitro DNA ejection in bacteriophage lambda. Past work has demonstrated that bacteriophage DNA is highly pressurized; this pressure has been hypothesized to help drive DNA ejection. Ions influence this process by screening charges on DNA; however, a systematic variation of salt concentrations to explore these effects has not been undertaken. To study the nature of the forces driving DNA ejection, we performed in vitro measurements of DNA ejection in bulk and at the single-phage level. We present measurements on the dynamics of ejection and on the self-repulsion force driving ejection. We examine the role of ion concentration and identity in both measurements, and show that the charge of counter-ions is an important control parameter. These measurements show that the frictional force acting on the ejecting DNA is subtly dependent on ionic concentrations for a given amount of DNA in the capsid. We also present evidence that phage DNA forms loops during ejection; we confirm that this effect occurs using optical tweezers. We speculate this facilitates circularization of the genome in the cytoplasm.Comment: David Wu and David Van Valen contributed equally to this project. 28 pages (including supplemental information), 4 figure

Rhodium(III) and iridium(III) complexes of a NHC-based macrocycle : persistent weak agostic interactions and reactions with dihydrogen

The synthesis and characterization of five-coordinate rhodium(III) and iridium(III) 2,2′-biphenyl complexes [M(CNC-12)(biph)][BArF4] (M = Rh (1a), Ir (1b)), featuring the macrocyclic lutidine- and NHC-based pincer ligand CNC-12 are reported. In the solid state these complexes are notable for the adoption of weak ε-agostic interactions that are characterized by M···H–C contacts of ca. 3.0 Å by X-ray crystallography and ν(CH) bands of reduced wavenumber by ATR IR spectroscopy. Remarkably, these interactions persist on dissolution and were observed at room temperature using NMR spectroscopy (CD2Cl2) and solution-phase IR spectroscopy (CCl4). The associated metrics point toward a stronger M···H–C interaction in the iridium congener, and this conclusion is borne out on interrogation of 1 in silico using DFT-based NBO and QTAIM analyses. Reaction of 1 with dihydrogen resulted in hydrogenolysis of the biaryl and formation of fluxional hydride complexes, whose ground state formulations as [Rh(CNC-12)H2][BArF4] (2a″) and [Ir(CNC-12)H2(H2)][BArF4] (2b‴) are proposed on the basis of inversion recovery and variable-temperature NMR experiments, alongside a computational analysis. Reactions of 1 and 2 with carbon monoxide help support their respective structural properties

Impulsion d’embarquement et embarcation fatale

Le topos de l’embarquement vaut généralement amorce narrative. B. Traven, écrivant Le Vaisseau des morts (Das Totenschiff, 1926), diffère ce moment, qui devient central. Il fait courir sur quatre chapitres la scène-charnière où le narrateur rencontre un navire louche auquel, par un échange de dupes, il se lie. L’apparence d’une embarcation, funeste ou propice, s’avère ou se dément au fil du voyage: le pari sur la fortune du bateau est au programme du récit maritime. Mais qui miserait sur le mauvais ? Le discours pluriel du narrateur sur son embarquement est confus : il se dit libre ; néanmoins, on doute qu’il agisse proprio motu ; il finit par invoquer le destin. Démêler les forces en présence conduit à examiner le processus en vertu duquel, selon Traven, toute vie sera happée par un mécanisme inexorable. Dans Le Vaisseau des morts, la marginalisation d’un narrateur à l’identité ‘flottante’ donne prise aux recruteurs. Une conscience aiguë de l’agencement du piège, sur le plan énonciatif, le marquage d’une temporalité fatidique, sur le plan narratif, caractérisent l’unique roman maritime de Traven, initialement présenté comme « Histoire d’un marin américain »

Exact boundary conditions at finite distance for the time-dependent Schrodinger equation

Exact boundary conditions at finite distance for the solutions of the time-dependent Schrodinger equation are derived. A numerical scheme based on Crank-Nicholson method is proposed to illustrate its applicability in several examples.Comment: Latex.tar.gz file, 20 pages, 9 figure

Fontaines narratives de Jean GIono

[EN] In Jean Giono’s works, water assumes multiple aspects and fulfils crucial functions, although it is less described than air and light, the other major vital elements of which the narrator applies himself to rendering the fascinating ability to enliven things. Through a simple children scene, in « Jeux ou la naumachie », Giono reveals that the banks of flowing waters make the bed of fiction as well. From the contact with water spring at the same time the creatures and the creator. Fountain, stream, rain, river, sea... the various forms of water, endowed with personalities, correlate with other beings or metamorphoses. Their presence initiates a course of events, gives rise to flow or drift: the narration itself. Besides its genetic property, the gionien water distinguishes itself by its intermittent nature, as well as by three qualities generally associated; loud, sparkling and fragrant, aquatic matter reveals itself as a vibrating substance. This essential quality of being relates the element to the artist’s sensitive personality[ES] El agua, en la obra de Jean Giono, aunque menos descrita que el aire y la luz, elementos también vitales de los cuales el narrador se empeña en restituir el fascinante poder de animación, presenta múltiples aspectos y cumple funciones esenciales. A través de una sencilla escena de niños, Giono revela, en « Juegos o la naumaquia », como del lecho del agua viva nace la ficción, y como del contacto con el agua nacen al mismo tiempo las criaturas y el creador. Fuente, riachuelo, lluvia, rio, mar… todas las aguas, cada una con su personalidad, están en relación con otros seres o metamorfosis, y su presencia provoca un flujo de eventos, da lugar a una corriente, o deriva, como la narración misma. Más allá de su propiedad genética, el agua « gionesca » se distingue por su naturaleza intermitente, y por tres cualidades frecuentemente asociadas ; ruidosa, brillosa y fragante, la materia acuática aparece como una sustancia vibrante, cualidad esencial de la vida, que se relaciona con la personalidad sensible del artista.[FR] L’eau, dans l’œuvre de Jean Giono, quoique moins « décrite » que l’air et la lumière, autres éléments vitaux majeurs dont le conteur s’emploie à restituer le fascinant pouvoir d’animation, revêt de multiples aspects et assure des fonctions cruciales. Avec une simple scène d’enfants, Giono révèle, dans « Jeux ou la naumachie », que le lit d’eau vive fait celui de la fiction. Du contact avec l’eau naissent en même temps les créatures et le créateur. Fontaine, ruisseau, pluie, fleuve, mer... les diverses eaux, dotées d’une personnalité, sont corrélées à d’autres êtres ou à des métamorphoses. Leur présence amorce un cours d’événements, donne lieu à l’écoulement ou à la dérive : la narration même. Outre sa propriété génétique, l’eau gionienne se singularise par sa nature intermittente, ainsi que par trois qualités couramment associées ; bruyante, chatoyante et odorante, la matière aquatique apparaît comme une substance vibrante. Cette qualité primordiale de l’être apparente l’élément à la personnalité sensible de l’artiste.Leforestier, C. (2017). Fontaines narratives de Jean GIono. En Palabras e imaginarios del agua. Les mots et les imaginaires de léau. XXV coloquio AFUE. Editorial Universitat Politècnica de València. 467-473. https://doi.org/10.4995/XXVColloqueAFUE.2016.3039OCS46747

Jean Tardieu, le poème comme audiogramme

Perméable au bruissement perpétuel du monde, le sujet des poèmes de Jean Tardieu rend compte de cette perturbation majeure. Dans deux récits du recueil La première Personne du singulier (1952), « La Conversation » et la visite chez les Sauvage des « Trois souvenirs d’un figurant », le narrateur se présente comme un écouteur fasciné par une énigme sonore. L’examen de la première scène d’écoute met en évidence une vive sensibilité personnelle aux contrastes de la mimique vocale, aux modulations vocaliques qui communiquent les émotions humaines. La seconde scène, dont les protagonistes épient le flux et le reflux d’un bruit derrière une porte, révèle l’inquiétude et l’excitation que suscitent l’objet dérobé mais aussi l’éclosion du son, appréhendée comme une séparation. De la résonance, le sujet se délivre en émettant à son tour. La vocation poétique de Jean Tardieu paraît ainsi trouver son origine dans la nécessité de transcrire le rythme, murmure ou martèlement, qui lui parvient depuis toujours

The wave packet propagation using wavelets

It is demonstrated that the wavelets can be used to considerably speed up simulations of the wave packet propagation in multiscale systems. Extremely high efficiency is obtained in the representation of both bound and continuum states. The new method is compared with the fast Fourier algorithm. Depending on ratios of typical scales of a quantum system in question, the wavelet method appears to be faster by a few orders of magnitude.Comment: Latex 7 pages, 3 colored figures (Fig1 postscript, Fig2,3 gif) in files separate from the pape

Effect of different choices of the Boltzmannized flux operator on thermal exchange and recombination reactions

The rate constants for recombination and exchange reactions are calculated using the flux correlation approach with a general form of the Boltzmannized flux operator, which can simultaneously describe the Kubo and traditional half-split forms. First, we consider an exactly solvable model, i.e., the free particle case, in terms of a new scaling function. Next, as a non-trivial case, we study the recombination and exchange reactions at very high pressure. Since the rate constant is calculated by Laplace transform of the flux correlation function, the result depends on how the Boltzmannized flux operator is chosen. We find that a choice of the flux operator affects the rate constant considerably. For the recombination reaction, the ratio of the rate constant in the half-split form to that in the Kubo form approaches zero in the high pressure limit.Comment: 16 pages, including 8 figure

Shear Bond Strength of Self-Etching Adhesive Systems to Er:YAG Laser-Prepared Dentine with and without Pulpal Pressure Simulation

This is a copy of an article published in the Photomedicine and Laser Surgery © 2008 copyright Mary Ann Liebert, Inc.; Photomedicine and Laser Surgery is available online at: http://www.liebertonline.comInternational audienceObjective: This study was conducted to study the role of pulpal pressure on the shear bond strength of composite resin bonded to Er:YAG laser-prepared or bur-prepared dentine surfaces using a self-etching adhesive system. Materials and Methods: The occlusal surfaces of 80 human third molars were ground flat to expose the dentine. The dentine was prepared using either a carbide bur or an Er: YAG laser at 350 mJ/pulse and 10 Hz (fluence 44.5 J/cm(2)). Clearfil SE Bond was then applied with or without pressure. Rods of composite resin were bonded to dentine surfaces and shear bond tests were carried out. Results: When the Clearfil SE Bond was used without pressure, the difference between the shear bond strength values of bur-prepared and laser-prepared dentine surfaces was significant. When the Clearfil SE Bond was used with pressure, the difference of shear bond strength values was not significant between the two types of surface preparation. Conclusion: The absence of smear layer formation during the preparation of the dentine by the Er: YAG laser did not improve the adhesion values of self-etching adhesive systems