The effect of polydispersity on the ordering transition of adsorbed self-assembled rigid rods

Extensive Monte Carlo simulations were carried out to investigate the nature of the ordering transition of a model of adsorbed self-assembled rigid rods on the bonds of a square lattice [Tavares et. al., Phys. Rev E 79, 021505 (2009)]. The polydisperse rods undergo a continuous ordering transition that is found to be in the two-dimensional Ising universality class, as in models where the rods are monodisperse. This finding is in sharp contrast with the recent claim that equilibrium polydispersity changes the nature of the phase transition in this class of models [L`opez et. al., Phys. Rev E 80, 040105(R)(2009)].Comment: 19 pages, 5 figure

Lattice Model for water-solute mixtures

A lattice model for the study of mixtures of associating liquids is proposed. Solvent and solute are modeled by adapting the associating lattice gas (ALG) model. The nature of interaction solute/solvent is controlled by tuning the energy interactions between the patches of ALG model. We have studied three set of parameters, resulting on, hydrophilic, inert and hydrophobic interactions. Extensive Monte Carlo simulations were carried out and the behavior of pure components and the excess properties of the mixtures have been studied. The pure components: water (solvent) and solute, have quite similar phase diagrams, presenting: gas, low density liquid, and high density liquid phases. In the case of solute, the regions of coexistence are substantially reduced when compared with both the water and the standard ALG models. A numerical procedure has been developed in order to attain series of results at constant pressure from simulations of the lattice gas model in the grand canonical ensemble. The excess properties of the mixtures: volume and enthalpy as the function of the solute fraction have been studied for different interaction parameters of the model. Our model is able to reproduce qualitatively well the excess volume and enthalpy for different aqueous solutions. For the hydrophilic case, we show that the model is able to reproduce the excess volume and enthalpy of mixtures of small alcohols and amines. The inert case reproduces the behavior of large alcohols such as, propanol, butanol and pentanol. For last case (hydrophobic), the excess properties reproduce the behavior of ionic liquids in aqueous solution.Comment: 28 pages, 13 figure

Phase behavior of the Confined Lebwohl-Lasher Model

The phase behavior of confined nematogens is studied using the Lebwohl-Lasher model. For three dimensional systems the model is known to exhibit a discontinuous nematic-isotropic phase transition, whereas the corresponding two dimensional systems apparently show a continuous Berezinskii-Kosterlitz-Thouless like transition. In this paper we study the phase transitions of the Lebwohl-Lasher model when confined between planar slits of different widths in order to establish the behavior of intermediate situations between the pure planar model and the three-dimensional system, and compare with previous estimates for the critical thickness, i.e. the slit width at which the transition switches from continuous to discontinuous.Comment: Submitted to Physical Review

The condensation and ordering of models of empty liquids

We consider a simple model consisting of particles with four bonding sites ("patches"), two of type A and two of type B, on the square lattice, and investigate its global phase behavior by simulations and theory. We set the interaction between B patches to zero and calculate the phase diagram as the ratio between the AB and the AA interactions, {\epsilon}^\star_AB, varies. In line with previous work, on three-dimensional off-lattice models, we show that the liquid-vapor phase diagram exhibits a re-entrant or "pinched" shape for the same range of \epsilon^\star_AB, suggesting that the ratio of the energy scales - and the corresponding empty fluid regime - is independent of the dimensionality of the system and of the lattice structure. In addition, the model exhibits an order-disorder transition that is ferromagnetic in the re-entrant regime. The use of low-dimensional lattice models allows the simulation of sufficiently large systems to establish the nature of the liquid-vapor critical points and to describe the structure of the liquid phase in the empty fluid regime, where the size of the "voids" increases as the temperature decreases. We have found that the liquid-vapor critical point is in the 2D Ising universality class, with a scaling region that decreases rapidly as the temperature decreases. The results of simulations and theoretical analysis suggest that the line of order-disorder transitions intersects the condensation line at a multicritical point at zero temperature and density, for patchy particle models with a re-entrant, empty fluid, regime.Comment: 29 pagres, 9 figure

Lentiviral Vector-Mediated Correction of a Mouse Model of Leukocyte Adhesion Deficiency Type I

Leukocyte adhesion deficiency type I (LAD-I) is a primary immunodeficiency caused by mutations in the ITGB2 gene and is characterized by recurrent and life-threatening bacterial infections. These mutations lead to defective or absent expression of β2 integrins on the leukocyte surface, compromising adhesion and extravasation at sites of infection. Three different lentiviral vectors (LVs) conferring ubiquitous or preferential expression of CD18 in myeloid cells were constructed and tested in human and mouse LAD-I cells. All three hCD18-LVs restored CD18 and CD11a membrane expression in LAD-I patient-derived lymphoblastoid cells. Corrected cells recovered the ability to aggregate and bind to sICAM-1 after stimulation. All vectors induced stable hCD18 expression in hematopoietic cells from mice with a hypomorphic Itgb2 mutation (CD18(HYP)), both in vitro and in vivo after transplantation of corrected cells into primary and secondary CD18(HYP) recipients. hCD18(+) hematopoietic cells from transplanted CD18(HYP) mice also showed restoration of mCD11a surface co-expression. The analysis of in vivo neutrophil migration in CD18(HYP) mice subjected to two different inflammation models demonstrated that the LV-mediated gene therapy completely restored neutrophil extravasation in response to inflammatory stimuli. Finally, these vectors were able to correct the phenotype of human myeloid cells derived from CD34(+) progenitors defective in ITGB2 expression. These results support for the first time the use of hCD18-LVs for the treatment of LAD-I patients in clinical trials

Patient-Specific Prosthetic Fingers by Remote Collaboration - A Case Study

The concealment of amputation through prosthesis usage can shield an amputee from social stigma and help improve the emotional healing process especially at the early stages of hand or finger loss. However, the traditional techniques in prosthesis fabrication defy this as the patients need numerous visits to the clinics for measurements, fitting and follow-ups. This paper presents a method for constructing a prosthetic finger through online collaboration with the designer. The main input from the amputee comes from the Computer Tomography (CT) data in the region of the affected and the non-affected fingers. These data are sent over the internet and the prosthesis is constructed using visualization, computer-aided design and manufacturing tools. The finished product is then shipped to the patient. A case study with a single patient having an amputated ring finger at the proximal interphalangeal joint shows that the proposed method has a potential to address the patient's psychosocial concerns and minimize the exposure of the finger loss to the public.Comment: Open Access articl

Structure and relaxations in liquid and amorphous Selenium

We report a molecular dynamics simulation of selenium, described by a three-body interaction. The temperatures T_g and T_c and the structural properties are in agreement with experiment. The mean nearest neighbor coordination number is 2.1. A small pre-peak at about 1 AA^-1 can be explained in terms of void correlations. In the intermediate self-scattering function, i.e. the density fluctuation correlation, classical behavior, alpha- and beta-regimes, is found. We also observe the plateau in the beta-regime below T_g. In a second step, we investigated the heterogeneous and/or homogeneous behavior of the relaxations. At both short and long times the relaxations are homogeneous (or weakly heterogeneous). In the intermediate time scale, lowering the temperature increases the heterogeneity. We connect these different domains to the vibrational (ballistic), beta- and alpha-regimes. We have also shown that the increase in heterogeneity can be understood in terms of relaxations

Hydrodynamic bubble coarsening in off-critical vapour-liquid phase separation

Late-stage coarsening in off-critical vapour-liquid phase separation is re-examined. In the limit of bubbles of vapour distributed throughout a continuous liquid phase, it is argued that coarsening proceeds via inertial hydrodynamic bubble collapse. This replaces the Lifshitz-Slyozov-Wagner mechanism seen in binary liquid mixtures. The arguments are strongly supported by simulations in two dimensions using a novel single-component soft sphere fluid.Comment: 5 pages, 3 figures, revtex3.