Reversible Random Sequential Adsorption of Dimers on a Triangular Lattice

We report on simulations of reversible random sequential adsorption of dimers on three different lattices: a one-dimensional lattice, a two-dimensional triangular lattice, and a two-dimensional triangular lattice with the nearest neighbors excluded. In addition to the adsorption of particles at a rate K+, we allow particles to leave the surface at a rate K-. The results from the one-dimensional lattice model agree with previous results for the continuous parking lot model. In particular, the long-time behavior is dominated by collective events involving two particles. We were able to directly confirm the importance of two-particle events in the simple two-dimensional triangular lattice. For the two-dimensional triangular lattice with the nearest neighbors excluded, the observed dynamics are consistent with this picture. The two-dimensional simulations were motivated by measurements of Ca++ binding to Langmuir monolayers. The two cases were chosen to model the effects of changing pH in the experimental system.Comment: 9 pages, 10 figure

Adsorption of mono- and multivalent cat- and anions on DNA molecules

Adsorption of monovalent and multivalent cat- and anions on a deoxyribose nucleic acid (DNA) molecule from a salt solution is investigated by computer simulation. The ions are modelled as charged hard spheres, the DNA molecule as a point charge pattern following the double-helical phosphate strands. The geometrical shape of the DNA molecules is modelled on different levels ranging from a simple cylindrical shape to structured models which include the major and minor grooves between the phosphate strands. The densities of the ions adsorbed on the phosphate strands, in the major and in the minor grooves are calculated. First, we find that the adsorption pattern on the DNA surface depends strongly on its geometrical shape: counterions adsorb preferentially along the phosphate strands for a cylindrical model shape, but in the minor groove for a geometrically structured model. Second, we find that an addition of monovalent salt ions results in an increase of the charge density in the minor groove while the total charge density of ions adsorbed in the major groove stays unchanged. The adsorbed ion densities are highly structured along the minor groove while they are almost smeared along the major groove. Furthermore, for a fixed amount of added salt, the major groove cationic charge is independent on the counterion valency. For increasing salt concentration the major groove is neutralized while the total charge adsorbed in the minor groove is constant. DNA overcharging is detected for multivalent salt. Simulations for a larger ion radii, which mimic the effect of the ion hydration, indicate an increased adsorbtion of cations in the major groove.Comment: 34 pages with 14 figure

Study of the lineshape of the chi(c1) (3872) state

A study of the lineshape of the chi(c1) (3872) state is made using a data sample corresponding to an integrated luminosity of 3 fb(-1) collected in pp collisions at center-of-mass energies of 7 and 8 TeV with the LHCb detector. Candidate chi(c1)(3872) and psi(2S) mesons from b-hadron decays are selected in the J/psi pi(+)pi(-) decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the chi(c1 )(3872) and psi(2S) states, Delta m, and the width of the chi(c1 )(3872) state, Gamma(Bw), are determined to be (Delta m=185.598 +/- 0.067 +/- 0.068 Mev,)(Gamma BW=1.39 +/- 0.24 +/- 0.10 Mev,) where the first uncertainty is statistical and the second systematic. Using a Flatte-inspired model, the mode and full width at half maximum of the lineshape are determined to be (mode=3871.69+0.00+0.05 MeV.)(FWHM=0.22-0.04+0.13+0.07+0.11-0.06-0.13 MeV, ) An investigation of the analytic structure of the Flatte amplitude reveals a pole structure, which is compatible with a quasibound D-0(D) over bar*(0) state but a quasivirtual state is still allowed at the level of 2 standard deviations

Measurement of the CKM angle γγ in B±→DK±B^\pm\to D K^\pm and B±→Dπ±B^\pm \to D π^\pm decays with D→KS0h+h−D \to K_\mathrm S^0 h^+ h^-

A measurement of $CP$-violating observables is performed using the decays $B^\pm\to D K^\pm$ and $B^\pm\to D \pi^\pm$, where the $D$ meson is reconstructed in one of the self-conjugate three-body final states $K_{\mathrm S}\pi^+\pi^-$ and $K_{\mathrm S}K^+K^-$ (commonly denoted $K_{\mathrm S} h^+h^-$). The decays are analysed in bins of the $D$-decay phase space, leading to a measurement that is independent of the modelling of the $D$-decay amplitude. The observables are interpreted in terms of the CKM angle $\gamma$. Using a data sample corresponding to an integrated luminosity of $9\,\text{fb}^{-1}$ collected in proton-proton collisions at centre-of-mass energies of $7$, $8$, and $13\,\text{TeV}$ with the LHCb experiment, $\gamma$ is measured to be $\left(68.7^{+5.2}_{-5.1}\right)^\circ$. The hadronic parameters $r_B^{DK}$, $r_B^{D\pi}$, $\delta_B^{DK}$, and $\delta_B^{D\pi}$, which are the ratios and strong-phase differences of the suppressed and favoured $B^\pm$ decays, are also reported

Translational molecular diffusion in phospholipid monolayers : substrate coupling and phase transitions

The results of an investigation of the phases of a monolayer of the phospholipid dipalmitoylphosphatidylcholine, deposited by Langmuir-Blodgett techniques onto hydrocarbon-derivatized silicon substrates, are described Measurements of the long-range translational diffusion of fluorescent lipid analogs in such monolayers reveal the presence of a phase transition not previously seen in phospholipids. It is marked by a large increase of lipid mobility at a temperature characteristic of the employed combination of lipid and substrate-attached hydrocarbon residue. A second transition into a high temperature phase, characterized by a rapid, homogeneous diffusivity, is observed at a temperature slightly above the temperature of the so-called chain melting transition in hydrated multi-bilayers of the lipid. In the novel intermediate state between the two transitions, long-range translational diffusion in the uniformly fluorescent monolayers is best described in a manner analogous to transport in composite materials. Lipid analogs containing a fluorophore in the polar headgroup portion of the molecule sample coexisting populations of host lipid whose diffusivities differ by as much as an order of magnitude in this temperature range. A chain labelled lipid analog is found to exhibit completely different behaviour, remaining largely immobile on the scale of the experimental observation times at temperatures below 43 °C. In samples cycled through the high temperature phase, this label exhibits increased mobilities at lower temperatures for several hours before returning to its original state. The measured diffusivities are compared with corresponding values obtained for monolayers spread at the air-water interface for which the average density is fixed, and also with available data for hydrated multibilayers. In natural bilayer membranes the two monolayer leaflets are generally not identical. They thus exhibit the same type of asymmetry as the one inherent in the system described here.Nous donnons les résultats d'une étude des phases de monocouches de la lécithine dipalmitoyl. Celles-ci sont déposées, par la technique de Langmuir-Blodgett, sur un substrat siliconé ponté de chaînes hydrocarbonées. Les mesures du coefficient de diffusion translationnel d'un analogue lipidique fluorescent mettent en évidence une transition de phase jusqu'ici non observée. Cette transition implique une augmentation notable de la mobilité lipidique du système considéré. Une seconde transition caractérisée par une rapide diffusion homogène (D ≽ 5 x 10-8 cm2/s) est observée pour une température supérieure à celle de la transition pour multicouches en smectique A. Le domaine de diffusion translationnelle ainsi mis en évidence est décrit par analogie au transport de masse dans un matériau hétérogène. Dans cette gamme de température, l'analogue lipidique, porteur du fluorophore sur sa portion polaire, discrimine deux populations de la couche hôte. Leurs coefficients de diffusion diffèrent d'un ordre de grandeur. Pourtant un analogue lipidique marqué sur la chaîne se trouve être pratiquement immobile dans l'échelle de temps d'expérimentation et pour des températures au-dessous de 43 °C. Dans le cas d'échantillons portés à hautes températures, puis refroidis, ces lipides marqués conservent une mobilité importante pour des températures basses et cela durant plusieurs heures avant de rétablir leur état diffusif initial. De plus, les mesures du coefficient de diffusion sont comparées à celles obtenues pour des monocouches à une interface air-eau de densité donnée ainsi qu'à celles de multicouches hydratées. Dans le cas de membranes naturelles à constituants essentiellement lipidiques, les deux hémimembranes sont typiquement non identiques et, devraient aussi générer la même asymétrie que celle décrite dans cette étude

Coupling of Size and Shape Equilibration in Lipid Monolayer Domains

The time-dependent dynamics of domains formed in lipid monolayers has been investigated in the case of coexisting lipid phases of different molecular areas. In general, an applied nonequilibrium pressure gives rise to both size and shape changes of domains. In this work, it is shown how the two effects can be superposed, leading to transitions from circular domains to other shapes (such as harmonic modes n = 2,3,4.) depending on the value of the applied excess pressure. As the excess pressure changes, the symmetry numbers of the transitions change. The description of the transient states for the growth of circular domains allows one to predict the time for the appearance of the different n-fold distortions. It is shown how in principle a sequence of applied pressures can be used to produce domains with shapes derived from a given distortion symmetry, such as n = 2.SCOPUS: ar.jinfo:eu-repo/semantics/publishe