1
|
Demydiuk F, Solar M, Meyer H, Benzerara O, Paul W, Baschnagel J. Role of torsional potential in chain conformation, thermodynamics, and glass formation of simulated polybutadiene melts. J Chem Phys 2022; 156:234902. [PMID: 35732513 DOI: 10.1063/5.0094536] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
For polymer chains, the torsional potential is an important intramolecular energy influencing chain flexibility and segmental dynamics. Through molecular dynamics simulations of an atomistic model for melts of cis-trans-1,4-polybutadiene (PBD), we explore the effect of the torsions on conformational properties (bond vector correlations and mean-square internal distances), fundamental thermodynamic quantities (density, compressibility, internal energy, and specific heat), and glass transition temperature Tg. This is achieved by systematically reducing the strength of the torsional potential, starting from the chemically realistic chain (CRC) model with the full potential toward the freely rotating chain (FRC) model without the torsional potential. For the equilibrium liquid, we find that the effect of the torsions on polymer conformations is very weak. Still weaker is the influence on the monomer density ρ and isothermal compressibility κT of the polymer liquid, both of which can be considered as independent of the torsional potential. We show that a van der Waals-like model proposed by Long and Lequeux [Eur. Phys. J. E 4, 371 (2001)] allows us to describe very well the temperature (T) dependence of ρ and κT. We also find that our data obey the linear relation between 1/kBTρκT and 1/T (with the Boltzmann constant kB) that has recently been predicted and verified on the experiment by Mirigian and Schweizer [J. Chem. Phys. 140, 194507 (2014)]. For the equilibrium liquid, simulations result in a specific heat, at constant pressure and at constant volume, which increases on cooling. This T dependence is opposite to the one found experimentally for many polymer liquids, including PBD. We suggest that this difference between simulation and experiment may be attributed to quantum effects due to hydrogen atoms and backbone vibrations, which, by construction, are not included in the classical united-atom model employed here. Finally, we also determine Tg from the density-temperature curve monitored in a finite-rate cooling process. While the influence of the torsional potential on ρ(T) is vanishingly small in the equilibrium liquid, the effect of the torsions on Tg is large. We find that Tg decreases by about 150 K when going from the CRC to the FRC model.
Collapse
Affiliation(s)
- F Demydiuk
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| | - M Solar
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| | - H Meyer
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| | - O Benzerara
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| | - W Paul
- Institut für Physik, Martin Luther Universität, D-06099 Halle, Germany
| | - J Baschnagel
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| |
Collapse
|
2
|
Baglietto G, Seif A, Grigera TS, Paul W. Otherwise identical particles with differing, fixed speeds demix under time-reversible dynamics. Phys Rev E 2020; 101:062606. [PMID: 32688590 DOI: 10.1103/physreve.101.062606] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 05/26/2020] [Indexed: 11/07/2022]
Abstract
In recent years situations where elsewise identical particles demix when different degrees of freedom do not thermalize have become a research focus in nonequilibrium statistical mechanics. The majority of these models are formulated in the context of active particles, but the phenomenon also occurs for particles without driving. All the models studied so far share the property that they do not obey microscopic reversibility, and it may be thought that this is a necessary condition for such demixing to occur. We show here that such a demixing transition also occurs in a mixture of otherwise identical particles moving at two fixed but different speeds according to a time-reversible quasi-Newtonian dynamics. The mechanical instability underlying this behavior is generated by the lack of thermalization between the two subsystems, which is shared by all systems showing this behavior.
Collapse
Affiliation(s)
- G Baglietto
- Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB), CONICET y Universidad Nacional de La Plata, Calle 59 No. 789, B1900BTE La Plata, Argentina and CCT CONICET La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina
| | - A Seif
- Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB), CONICET y Universidad Nacional de La Plata, Calle 59 No. 789, B1900BTE La Plata, Argentina and CCT CONICET La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina
| | - T S Grigera
- Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB), CONICET y Universidad Nacional de La Plata, Calle 59 No. 789, B1900BTE La Plata, Argentina; CCT CONICET La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina; and Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina
| | - W Paul
- Institute of Physics, Martin-Luther University Halle-Wittenberg, 06099 Halle, Germany
| |
Collapse
|
3
|
Abstract
The competition between chain stiffness and chain collapse gives rise to complex low temperature morphologies of single polymer chains, in our case alkanes. These structures are characterized by specific sequences of dihedral angles along the chain, i.e., dihedral angle correlations extending beyond local steric effects. To describe and classify these morphologies, one can transfer concepts from protein science, where this creation of dihedral angle correlations underlies the formation of α-helices and β-sheets. We show here by means of flat-histogram Monte Carlo simulations that, although lacking in primary structure being simple homopolymers, short alkane chains fold into non-trivial ground states (tertiary structure) consisting of chain segments of defined secondary structures. The folded lamellar crystal typical for polyethylene chains requires a minimum chain length to occur as the ground state folded structure, which we identify to be around 150 repeat units.
Collapse
Affiliation(s)
- T Shakirov
- Institute of Physics, Martin Luther University, 06099 Halle, Germany
| | - W Paul
- Institute of Physics, Martin Luther University, 06099 Halle, Germany
| |
Collapse
|
4
|
Abstract
SummaryIn vivo platelet aggregation has been studied using a novel, minimally invasive technique. No aggregatory effects of heparin were observed on normal circulating platelets nor was there enhancement of aggregation of platelets during activation by fhtravenous injection of ADP, collagen, PAF acether or thrombin. On the contrary, high doses of heparin were found to inhibit platelet accumulation induced by ADP, collagen or PAF-acether. Inhibition of these responses necessitated doses of heparin in excess of those required for anti-coagulant effects. The present experiments do not establish a mechanism for such inhibition. Extension to other species, including man, is needed before attributing clinical relevance to the present observations.
Collapse
Affiliation(s)
- P A Barrett
- The Research Centre, Ciba-Geigy Pharmaceuticals Division, Horsham, West Sussex, U.K
| | - K D Butler
- The Research Centre, Ciba-Geigy Pharmaceuticals Division, Horsham, West Sussex, U.K
| | - J Morley
- The Department of Clinical Pharmacology, Cardiothoracic Institute, Brompton Hospital, London, U.K
| | - C P Page
- The Department of Clinical Pharmacology, Cardiothoracic Institute, Brompton Hospital, London, U.K
| | - W Paul
- The Department of Clinical Pharmacology, Cardiothoracic Institute, Brompton Hospital, London, U.K
| | - A M White
- The Research Centre, Ciba-Geigy Pharmaceuticals Division, Horsham, West Sussex, U.K
| |
Collapse
|
5
|
Abstract
SummaryA simple minimally invasive technique has been developed for the continuous monitoring of 111-Indium labelled homologous platelets in the thoracic (C1) and abdominal (C2) regions of experimental animals. The effects of the aggregatory agents adenosine diphosphate (ADP), collagen and platelet activating factor (PAF) and the anti-aggregatory agent, prostacyclin (PGI2) have been studied in the guinea-pig. Administration of ADP, collagen or PAF produces an increase in counts in C1, a decrease in counts in C2, and hence an increase in the ratio C1/C2. The rise in C1/C2 is more protracted after collagen administration than after ADP or PAF. PGI2 (50-500 ng/kg) reduces the response to ADP. The present technique is both simple, reproducible and although the present experiments are in the presence of heparin, the technique remains functional in the presence of minimal heparin, thus making it a suitable method for studies of platelet function and the evaluation of anti-aggregatory agents in vivo.
Collapse
Affiliation(s)
- C P Page
- The Department of Clinical Pharmacology (Asthma Research Council), Cardiothoracic Institute, London, U.K
| | - W Paul
- The Department of Clinical Pharmacology (Asthma Research Council), Cardiothoracic Institute, London, U.K
| | - J Morley
- The Department of Clinical Pharmacology (Asthma Research Council), Cardiothoracic Institute, London, U.K
| |
Collapse
|
6
|
Shakirov T, Paul W. Crystallization in melts of short, semiflexible hard polymer chains: An interplay of entropies and dimensions. Phys Rev E 2018; 97:042501. [PMID: 29758595 DOI: 10.1103/physreve.97.042501] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Indexed: 12/19/2022]
Abstract
What is the thermodynamic driving force for the crystallization of melts of semiflexible polymers? We try to answer this question by employing stochastic approximation Monte Carlo simulations to obtain the complete thermodynamic equilibrium information for a melt of short, semiflexible polymer chains with purely repulsive nonbonded interactions. The thermodynamics is obtained based on the density of states of our coarse-grained model, which varies by up to 5600 orders of magnitude. We show that our polymer melt undergoes a first-order crystallization transition upon increasing the chain stiffness at fixed density. This crystallization can be understood by the interplay of the maximization of different entropy contributions in different spatial dimensions. At sufficient stiffness and density, the three-dimensional orientational interactions drive the orientational ordering transition, which is accompanied by a two-dimensional translational ordering transition in the plane perpendicular to the chains resulting in a hexagonal crystal structure. While the three-dimensional ordering can be understood in terms of Onsager theory, the two-dimensional transition can be understood in terms of the liquid-hexatic transition of hard disks. Due to the domination of lateral two-dimensional translational entropy over the one-dimensional translational entropy connected with columnar displacements, the chains form a lamellar phase. Based on this physical understanding, orientational ordering and translational ordering should be separable for polymer melts. A phenomenological theory based on this understanding predicts a qualitative phase diagram as a function of volume fraction and stiffness in good agreement with results from the literature.
Collapse
Affiliation(s)
- T Shakirov
- Institute of Physics, Martin-Luther-University, 06099 Halle, Germany
| | - W Paul
- Institute of Physics, Martin-Luther-University, 06099 Halle, Germany
| |
Collapse
|
7
|
Solar M, Binder K, Paul W. Relaxation processes and glass transition of confined polymer melts: A molecular dynamics simulation of 1,4-polybutadiene between graphite walls. J Chem Phys 2018; 146:203308. [PMID: 28571361 DOI: 10.1063/1.4975390] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Molecular dynamics simulations of a chemically realistic model for 1,4-polybutadiene in a thin film geometry confined by two graphite walls are presented. Previous work on melts in the bulk has shown that the model faithfully reproduces static and dynamic properties of the real material over a wide temperature range. The present work studies how these properties change due to nano-confinement. The focus is on orientational correlations observable in nuclear magnetic resonance experiments and on the local intermediate incoherent neutron scattering function, Fs(qz, z, t), for distances z from the graphite walls in the range of a few nanometers. Temperatures from about 2Tg down to about 1.15Tg, where Tg is the glass transition temperature in the bulk, are studied. It is shown that weakly attractive forces between the wall atoms and the monomers suffice to effectively bind a polymer coil that is near the wall. For a wide regime of temperatures, the Arrhenius-like adsorption/desorption kinetics of the monomers is the slowest process, while very close to Tg the Vogel-Fulcher-Tammann-like α-relaxation takes over. The α-process is modified only for z≤1.2 nm due to the density changes near the walls, less than expected from studies of coarse-grained (bead-spring-type) models. The weakness of the surface effects on the glass transition in this case is attributed to the interplay of density changes near the wall with the torsional potential. A brief discussion of pertinent experiments is given.
Collapse
Affiliation(s)
- M Solar
- Institut Charles Sadron, Université Strasbourg, F-67034 Strasbourg, France
| | - K Binder
- Institut für Physik, Johannes Gutenberg-Universität, D-55099 Mainz, Germany
| | - W Paul
- Institut für Physik, Martin Luther-Universität, D-06099 Halle, Germany
| |
Collapse
|
8
|
|
9
|
Ricks PM, Hershow RC, Rahimian A, Huo D, Johnson W, Prachand N, Jimenez A, Wiebel W, Paul W. A randomized trial comparing standard outcomes in two treatment models for substance users with tuberculosis. Int J Tuberc Lung Dis 2015; 19:326-32. [PMID: 25686142 DOI: 10.5588/ijtld.14.0471] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
SETTING Chicago Department of Public Health (CDPH), TB Control Program. OBJECTIVES To compare anti-tuberculosis treatment outcomes using two different types of directly observed therapy (DOT) outreach workers. METHODS Substance users diagnosed with TB from October 1996 to July 2000 were randomized to DOT administered by either 1) CDPH personnel (standard arm) or 2) previous substance-using human immunodeficiency virus/acquired immune-deficiency syndrome outreach workers (enhanced arm). Treatment completion was physician-determined, and adherence was estimated based on risk of missed DOT appointments. RESULTS Of 94 patients, 46 were randomized to the standard and 48 to the enhanced arm. The standard arm had a significantly higher risk of non-completion of treatment (39% vs. 15%, RR 2.7, 95%CI 1.2-5.8), and a significantly higher risk of missing DOT appointments (RR 2.6, 95%CI 1.4-4.8). For both outcomes, housing instability was a significant predictor in multivariate analyses. CONCLUSIONS TB treatment completion and adherence among substance users was improved by the enhanced intervention; the familiarity of enhanced-arm DOT workers with the patients' social norms due to their own previous substance use may have made them more effective. Successful DOT in hard-to-reach populations may require strategies that directly address the population's circumstances and utilize DOT workers who are intimately familiar with patients' life situations.
Collapse
Affiliation(s)
- P M Ricks
- School of Public Health, University of Illinois at Chicago, Chicago, Illinois, USA
| | - R C Hershow
- School of Public Health, University of Illinois at Chicago, Chicago, Illinois, USA
| | - A Rahimian
- Independent Researcher, Seattle, Washington, USA
| | - D Huo
- Department of Health Studies, University of Chicago Chicago, Illinois, USA
| | - W Johnson
- Georgia Perimeter College, Fairburn, Georgia, USA
| | - N Prachand
- Chicago Department of Health, Chicago, Illinois, USA
| | - A Jimenez
- School of Public Health, University of Illinois at Chicago, Chicago, Illinois, USA
| | - W Wiebel
- School of Public Health, University of Illinois at Chicago, Chicago, Illinois, USA
| | - W Paul
- Metro Public Health Department of Nashville/Davidson County, Nashville, Tennessee, USA
| |
Collapse
|
10
|
Baumann S, Donati F, Stepanow S, Rusponi S, Paul W, Gangopadhyay S, Rau IG, Pacchioni GE, Gragnaniello L, Pivetta M, Dreiser J, Piamonteze C, Lutz CP, Macfarlane RM, Jones BA, Gambardella P, Heinrich AJ, Brune H. Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO. Phys Rev Lett 2015; 115:237202. [PMID: 26684139 DOI: 10.1103/physrevlett.115.237202] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Indexed: 06/05/2023]
Abstract
We report on the magnetic properties of individual Fe atoms deposited on MgO(100) thin films probed by x-ray magnetic circular dichroism and scanning tunneling spectroscopy. We show that the Fe atoms have strong perpendicular magnetic anisotropy with a zero-field splitting of 14.0±0.3 meV/atom. This is a factor of 10 larger than the interface anisotropy of epitaxial Fe layers on MgO and the largest value reported for Fe atoms adsorbed on surfaces. The interplay between the ligand field at the O adsorption sites and spin-orbit coupling is analyzed by density functional theory and multiplet calculations, providing a comprehensive model of the magnetic properties of Fe atoms in a low-symmetry bonding environment.
Collapse
Affiliation(s)
- S Baumann
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - F Donati
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - S Stepanow
- Department of Materials, ETH Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland
| | - S Rusponi
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - W Paul
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - S Gangopadhyay
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
- Department of Physics, University of California, Davis, California 95616, USA
| | - I G Rau
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - G E Pacchioni
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - L Gragnaniello
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - M Pivetta
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - J Dreiser
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
- Swiss Light Source (SLS), Paul Scherrer Institute (PSI), CH-5232 Villigen PSI, Switzerland
| | - C Piamonteze
- Swiss Light Source (SLS), Paul Scherrer Institute (PSI), CH-5232 Villigen PSI, Switzerland
| | - C P Lutz
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - R M Macfarlane
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - B A Jones
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - P Gambardella
- Department of Materials, ETH Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland
| | - A J Heinrich
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - H Brune
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| |
Collapse
|
11
|
Gnanachandran C, Paul W. A Retrospective Descriptive Comparison Study of Transvaginal Ultrasound Scan Findings With Histology Findings on Postmenopausal Women Who Underwent Hysteroscopy for Endometrial Assessment. J Minim Invasive Gynecol 2015; 22:S50. [DOI: 10.1016/j.jmig.2015.08.137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
|
12
|
|
13
|
Solar M, Paul W. Dielectric α-relaxation of 1,4-polybutadiene confined between graphite walls : Molecular dynamics investigations through numerical simulations of polymer molecules relaxation. Eur Phys J E Soft Matter 2015; 38:123. [PMID: 25967943 DOI: 10.1140/epje/i2015-15037-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2015] [Revised: 03/11/2015] [Accepted: 03/11/2015] [Indexed: 06/04/2023]
Abstract
We present results of Molecular Dynamics (MD) simulations of a chemically realistic model of 1,4-polybutadiene confined by crystalline graphite walls. The simulations cover a large range of temperatures from T ≈ 2T g to T ≈ 1.15T g, where relevant time scales are accessible using such computational methods. We investigate the dielectric relaxation close to the walls in comparison to the one in the center of the film, and study the latter as a function of the film thickness from the walls. The segmental dynamics in the film is slowed down close to the walls, in comparison to the bulk. In addition to the α-process, the relaxation exhibits an additional long time decay, the so-called wall desorption process. We focus here on the α-process and find no significant shift of the dielectric T g as a function of layer thickness, in agreement with recent dielectric experiments. These findings can be correlated with the importance of the dihedral dynamics for all relaxation processes in polymers, which is unaltered except for the first nanometer next to the walls.
Collapse
Affiliation(s)
- M Solar
- Institut Charles Sadron (UPR22-CNRS), University of Strasbourg, 23 rue du Loess, BP 84047, F-67034, Strasbourg, France,
| | | |
Collapse
|
14
|
Kuhnhold A, Paul W. Active one-particle microrheology of an unentangled polymer melt studied by molecular dynamics simulation. Phys Rev E Stat Nonlin Soft Matter Phys 2015; 91:042601. [PMID: 25974519 DOI: 10.1103/physreve.91.042601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Indexed: 06/04/2023]
Abstract
We present molecular dynamics simulations for active one-particle microrheology of an unentangled polymer melt. The tracer particle is forced to oscillate by an oscillating harmonic potential, which models an experiment using optical tweezers. The amplitude and phase shift of this oscillation are related to the complex shear modulus of the polymer melt. In the linear response regime at low frequencies, the active microrheology gives the same result as the passive microrheology, where the thermal motion of a tracer particle is related to the complex modulus. We expand the analysis to include full hydrodynamic effects instead of stationary Stokes friction only, and show that different approaches suggested in the literature lead to completely different results, and that none of them improves on the description using the stationary Stokes friction.
Collapse
Affiliation(s)
- A Kuhnhold
- Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle (Saale), Germany
| | - W Paul
- Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle (Saale), Germany
| |
Collapse
|
15
|
Kuhnhold A, Paul W. Temperature dependent micro-rheology of a glass-forming polymer melt studied by molecular dynamics simulation. J Chem Phys 2014; 141:124907. [DOI: 10.1063/1.4896151] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
16
|
Kuhnhold A, Paul W. Passive one-particle microrheology of an unentangled polymer melt studied by molecular dynamics simulation. Phys Rev E Stat Nonlin Soft Matter Phys 2014; 90:022602. [PMID: 25215751 DOI: 10.1103/physreve.90.022602] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Indexed: 06/03/2023]
Abstract
We present a molecular dynamics simulation study of the possibility of performing a microrheological analysis of a polymer melt by following the Brownian motion of a dispersed nanoparticle. We study the influence of the size of the nanoparticle, taken to be comparable to the radius of gyration of the chains, and of the strength of the interaction between the nanoparticle and the repeat units of the polymer chains. The influence of the presence of the nanoparticle on the melt mechanical behavior is analyzed, and the importance of effects of different levels of hydrodynamic analysis on the frequency-dependent dynamic shear modulus derived from the particle motion is worked out.
Collapse
Affiliation(s)
- A Kuhnhold
- Institut für Physik, Martin-Luther-Universität, Halle-Wittenberg, 06099 Halle (Saale), Germany
| | - W Paul
- Institut für Physik, Martin-Luther-Universität, Halle-Wittenberg, 06099 Halle (Saale), Germany
| |
Collapse
|
17
|
Oliver DJ, Paul W, El Ouali M, Hagedorn T, Miyahara Y, Qi Y, Grütter PH. One-to-one spatially matched experiment and atomistic simulations of nanometre-scale indentation. Nanotechnology 2014; 25:025701. [PMID: 24334512 DOI: 10.1088/0957-4484/25/2/025701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We have carried out nanoindentation studies of gold in which the indenter is atomically characterized by field-ion microscopy and the scale of deformation is sufficiently small to be directly compared with atomistic simulations. We find that many features of the experiment are correctly reproduced by molecular dynamics simulations, in some cases only when an atomically rough indenter rather than a smooth repulsive-potential indenter is used. Heterogeneous nucleation of dislocations is found to take place at surface defect sites. Using input from atomistic simulations, a model of indentation based on stochastic transitions between continuum elastic-plastic states is developed, which accurately predicts the size distributions of plastic 'pop-in' events and their dependence on tip geometry.
Collapse
Affiliation(s)
- D J Oliver
- Department of Physics, McGill University, Montreal, QC H3A2T8, Canada
| | | | | | | | | | | | | |
Collapse
|
18
|
Ivanov VA, Rodionova AS, Martemyanova JA, Stukan MR, Müller M, Paul W, Binder K. Wall-induced orientational order in athermal semidilute solutions of semiflexible polymers: Monte Carlo simulations of a lattice model. J Chem Phys 2013; 138:234903. [DOI: 10.1063/1.4810745] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
19
|
Fasano RM, Paul W, Siegal E, Luban NLC. Transfusion protocol for patients with sickle hemoglobinopathies at Children's National Medical Center. Immunohematology 2012; 28:13-16. [PMID: 22646144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Affiliation(s)
- R M Fasano
- Chronic Transfusion Program, Division of Hematology, Transfusion Medicine, Children's National Medical Center, Washington, DC, USA
| | | | | | | |
Collapse
|
20
|
Ivanov VA, Rodionova AS, An EA, Martemyanova JA, Stukan MR, Müller M, Paul W, Binder K. Orientational ordering transitions of semiflexible polymers in thin films: a Monte Carlo simulation. Phys Rev E Stat Nonlin Soft Matter Phys 2011; 84:041810. [PMID: 22181168 DOI: 10.1103/physreve.84.041810] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Indexed: 05/31/2023]
Abstract
Athermal solutions (from dilute to concentrated) of semiflexible macromolecules confined in a film of thickness D between two hard walls are studied by means of grand-canonical lattice Monte Carlo simulation using the bond fluctuation model. This system exhibits two phase transitions as a function of the thickness of the film and polymer volume fraction. One of them is the bulk isotropic-nematic first-order transition, which ends in a critical point on decreasing the film thickness. The chemical potential at this transition decreases with decreasing film thickness ("capillary nematization"). The other transition is a continuous (or very weakly first-order) transition in the layers adjacent to the hard planar walls from the disordered phase, where the bond vectors of the macromolecules show local ordering (i.e., "preferential orientation" along the x or y axes of the simple cubic lattice, but no long-range orientational order occurs), to a quasi-two-dimensional nematic phase (with the director at each wall being oriented along either the x or y axis), while the bulk of the film is still disordered. When the chemical potential or monomer density increase, respectively, the thickness of these surface-induced nematic layers grows, causing the disappearance of the disordered region in the center of the film.
Collapse
Affiliation(s)
- V A Ivanov
- Faculty of Physics, Moscow State University, Moscow 119991, Russia
| | | | | | | | | | | | | | | |
Collapse
|
21
|
Theodorakis PE, Paul W, Binder K. Analysis of the cluster formation in two-component cylindrical bottle-brush polymers under poor solvent conditions: a simulation study. Eur Phys J E Soft Matter 2011; 34:52. [PMID: 21607832 DOI: 10.1140/epje/i2011-11052-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Accepted: 05/09/2011] [Indexed: 05/30/2023]
Abstract
Two-component bottle-brush polymers, where flexible side chains containing N = 20, 35 and 50 effective monomers are grafted alternatingly to a rigid backbone, are studied by Molecular Dynamics simulations, varying the grafting density [Formula: see text] and the solvent quality. Whereas for poor solvents and large enough [Formula: see text] the molecular brush is a cylindrical object with monomers of different type occupying locally the two different halves of the cylinder, for intermediate values of [Formula: see text] an axially inhomogeneous structure of "pearl-necklace" type is formed, where microphase separation between monomers of different type within a cluster takes place. These "pearls" have a strongly non-spherical ellipsoidal shape, due to the fact that several side chains cluster together in one "pearl". We discuss the resulting structures in detail and we present a comparison with the single-component bottle-brush case.
Collapse
Affiliation(s)
- P E Theodorakis
- Institut für Physik, Johannes Gutenberg-Universität, Mainz, Germany.
| | | | | |
Collapse
|
22
|
|
23
|
Bork VP, Fedders PA, Norberg RE, Leopold DJ, Mackenzie KD, Paul W. Deuteron Magnetic Resonance in a-Si and a-SiGe Produced from Fluorides. ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-70-307] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
ABSTRACTDeuteron magnetic resonance line shapes and spin lattice relaxation times are presented for a-Si:D, F and a-SiGe:D, F. These parameters differ from those for typical a-Si:D, H samples, but in some respects are similar to those for an annealed a-Si:D, H sample. The a-SiGe:D, F spectra display an unusually large broad central weakly bound D resonance component and a barely-resolved Ge-D quadrupolar doublet. Comparisons indicate substantial differences in void morphology between the a-Si:D, F and a-SiGe:D, F.
Collapse
|
24
|
Labuda A, Brastaviceanu T, Pavlov I, Paul W, Rassier DE. Optical detection system for probing cantilever deflections parallel to a sample surface. Rev Sci Instrum 2011; 82:013701. [PMID: 21280831 DOI: 10.1063/1.3527913] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
To date, commercial atomic force microscopes have been optimized for measurements of forces perpendicular to the sample surface. In many applications, sensitive parallel force measurements are desirable. These can be obtained by positioning the cantilever with its long axis perpendicular to the sample: the so-called pendulum geometry. We present a compact optical beam deflection system which solves the geometrical constraint problems involved in focusing a light beam onto a cantilever in the pendulum geometry. We demonstrate the performance of the system on measurements of forces imparted by a muscle myofibril, which is in-plane to a high-magnification objective of an optical microscope.
Collapse
Affiliation(s)
- A Labuda
- Department of Physics, Faculty of Science, McGill University, Montreal, Canada
| | | | | | | | | |
Collapse
|
25
|
Vallée RAL, Paul W, Binder K. Single Molecules Probing the Freezing of Polymer Melts: A Molecular Dynamics Study for Various Molecule-Chain Linkages. Macromolecules 2010. [DOI: 10.1021/ma101975j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- R. A. L. Vallée
- Centre de Recherche Paul Pascal (CNRS), 115 avenue du docteur Albert Schweitzer, 33600 Pessac, France
| | - W. Paul
- Institut für Physik, Martin-Luther University, 06099 Halle, Germany
| | - K. Binder
- Institut für Physik, Johannes-Gutenberg University, 55099 Mainz, Germany
| |
Collapse
|
26
|
Yelash L, Virnau P, Binder K, Paul W. Slow process in confined polymer melts: layer exchange dynamics at a polymer solid interface. Phys Rev E Stat Nonlin Soft Matter Phys 2010; 82:050801. [PMID: 21230426 DOI: 10.1103/physreve.82.050801] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2010] [Revised: 08/27/2010] [Indexed: 05/30/2023]
Abstract
Employing Molecular Dynamics simulations of a chemically realistic model of 1,4-polybutadiene between graphite walls we show that the mass exchange between layers close to the walls is a slow process already in the melt state. For the glass transition of confined polymers this process competes with the slowing down due to packing effects and intramolecular rotation barriers.
Collapse
Affiliation(s)
- L Yelash
- Institute of Physics, Johannes-Gutenberg-University, 55099 Mainz, Germany
| | | | | | | |
Collapse
|
27
|
Beccaro MAD, Villanueva R, Knudson KM, Harvey EM, Langle JM, Paul W. Decision Support Alerts for Medication Ordering in a Computerized Provider Order Entry (CPOE) System: A systematic approach to decrease alerts. Appl Clin Inform 2010; 1:346-62. [PMID: 23616845 DOI: 10.4338/aci-2009-11-ra-0014] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2009] [Accepted: 09/07/2010] [Indexed: 11/23/2022] Open
Abstract
OBJECTIVE We sought to determine the frequency and type of decision support alerts by location and ordering provider role during Computerized Provider Order Entry (CPOE) medication ordering. Using these data we adjusted the decision support tools to reduce the number of alerts. DESIGN Retrospective analyses were performed of dose range checks (DRC), drug-drug interaction and drug-allergy alerts from our electronic medical record. During seven sampling periods (each two weeks long) between April 2006 and October 2008 all alerts in these categories were analyzed. Another audit was performed of all DRC alerts by ordering provider role from November 2008 through January 2009. Medication ordering error counts were obtained from a voluntary error reporting system. MEASUREMENTRESULTS: Between April 2006 and October 2008 the percent of medication orders that triggered a dose range alert decreased from 23.9% to 7.4%. The relative risk (RR) for getting an alert was higher at the start of the interventions versus later (RR= 2.40, 95% CI 2.28-2.52; p< 0.0001). The percentage of medication orders that triggered alerts for drug-drug interactions also decreased from 13.5% to 4.8%. The RR for getting a drug interaction alert at the start was 1.63, 95% CI 1.60-1.66; p< 0.0001. Alerts decreased in all clinical areas without an increase in reported medication errors. CONCLUSION We reduced the quantity of decision support alerts in CPOE using a systematic approach without an increase in reported medication errors.
Collapse
|
28
|
Theodorakis PE, Paul W, Binder K. Pearl-necklace structures of molecular brushes with rigid backbone under poor solvent conditions: A simulation study. J Chem Phys 2010; 133:104901. [PMID: 20849186 DOI: 10.1063/1.3477981] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- P E Theodorakis
- Institut für Physik, Johannes Gutenberg-Universität, Staudinger Weg 7, Mainz D-55099, Germany.
| | | | | |
Collapse
|
29
|
Paul W. CD4 T cells: fates and functions (ML05). Int Immunol 2010. [DOI: 10.1093/intimm/dxq098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
|
30
|
Rading D, Moellers R, Kollmer F, Paul W, Niehuis E. Dual beam depth profiling of organic materials: Variations of analysis and sputter beam conditions. SURF INTERFACE ANAL 2010. [DOI: 10.1002/sia.3422] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
|
31
|
|
32
|
Vallée RAL, Paul W, Binder K. Probe molecules in polymer melts near the glass transition: A molecular dynamics study of chain length effects. J Chem Phys 2010; 132:034901. [PMID: 20095750 DOI: 10.1063/1.3284780] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- R A L Vallée
- Centre de Recherche Paul Pascal (CNRS), 115 Avenue du Docteur Albert Schweitzer, 33600 Pessac, France
| | | | | |
Collapse
|
33
|
Kerger H, Paul W, Wild H. [On the myopic effect of Pilocarpin (1 per cent)-, Jestryl (Doryl) (1 per cent)- and Neoserin (Prostigmin) (3 per cent)-eyedrops]. Acta Ophthalmol 2009; 47:189-201. [PMID: 5819825 DOI: 10.1111/j.1755-3768.1969.tb05622.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
|
34
|
Mognetti BM, Virnau P, Yelash L, Paul W, Binder K, Müller M, MacDowell LG. Coarse-grained models for fluids and their mixtures: Comparison of Monte Carlo studies of their phase behavior with perturbation theory and experiment. J Chem Phys 2009; 130:044101. [DOI: 10.1063/1.3050353] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
|
35
|
New HV, Stanworth SJ, Engelfriet CP, Reesink HW, McQuilten ZK, Savoia HF, Wood EM, Olyntho S, Trigo F, Wendel S, Lin Y, Hume H, Petäjä J, Krusius T, Villa S, Ghirardello S, von Lindern J, Brand A, Hendrickson JE, Josephson CD, Strauss RG, Luban NLC, Paul W. Neonatal transfusions. Vox Sang 2009; 96:62-85. [DOI: 10.1111/j.1423-0410.2008.01105.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
|
36
|
Mognetti BM, Virnau P, Yelash L, Paul W, Binder K, Müller M, MacDowell LG. Coarse-graining dipolar interactions in simple fluids and polymer solutions: Monte Carlo studies of the phase behavior. Phys Chem Chem Phys 2009; 11:1923-33. [DOI: 10.1039/b818020m] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
|
37
|
|
38
|
Gonick H, Paul W, Sommers S, Guze L. Functional Studies in Experimental Pyelonephritis. Nephron Clin Pract 2008. [DOI: 10.1159/000179575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
|
39
|
Ivanov VA, Martemyanova JA, Müller M, Paul W, Binder K. Conformational Changes of a Single Semiflexible Macromolecule Near an Adsorbing Surface: A Monte Carlo Simulation. J Phys Chem B 2008; 113:3653-68. [DOI: 10.1021/jp806348y] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- V. A. Ivanov
- Faculty of Physics, Moscow State University, 119992 Moscow, Russia, Institut für Theoretische Physik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany, and Institut für Physik, Johannes-Gutenberg-Universität Mainz, Staudinger Weg 7, 55099 Mainz, Germany
| | - J. A. Martemyanova
- Faculty of Physics, Moscow State University, 119992 Moscow, Russia, Institut für Theoretische Physik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany, and Institut für Physik, Johannes-Gutenberg-Universität Mainz, Staudinger Weg 7, 55099 Mainz, Germany
| | - M. Müller
- Faculty of Physics, Moscow State University, 119992 Moscow, Russia, Institut für Theoretische Physik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany, and Institut für Physik, Johannes-Gutenberg-Universität Mainz, Staudinger Weg 7, 55099 Mainz, Germany
| | - W. Paul
- Faculty of Physics, Moscow State University, 119992 Moscow, Russia, Institut für Theoretische Physik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany, and Institut für Physik, Johannes-Gutenberg-Universität Mainz, Staudinger Weg 7, 55099 Mainz, Germany
| | - K. Binder
- Faculty of Physics, Moscow State University, 119992 Moscow, Russia, Institut für Theoretische Physik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany, and Institut für Physik, Johannes-Gutenberg-Universität Mainz, Staudinger Weg 7, 55099 Mainz, Germany
| |
Collapse
|
40
|
Affiliation(s)
- K. Binder
- Institut für Physik, Johannes Gutenberg-Universität, Staudinger Weg 7, D-55099 Mainz, Germany
| | - W. Paul
- Institut für Physik, Johannes Gutenberg-Universität, Staudinger Weg 7, D-55099 Mainz, Germany
| |
Collapse
|
41
|
Mognetti BM, Oettel M, Yelash L, Virnau P, Paul W, Binder K. Spherically averaged versus angle-dependent interactions in quadrupolar fluids. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 77:041506. [PMID: 18517627 DOI: 10.1103/physreve.77.041506] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2008] [Indexed: 05/26/2023]
Abstract
Employing simplified models in computer simulation is on the one hand often enforced by computer time limitations but on the other hand it offers insights into the molecular properties determining a given physical phenomenon. We employ this strategy to the determination of the phase behavior of quadrupolar fluids, where we study the influence of omitting angular degrees of freedom of molecules via an effective spherically symmetric potential obtained from a perturbative expansion. Comparing the liquid-vapor coexistence curve, vapor pressure at coexistence, interfacial tension between the coexisting phases, etc., as obtained from both the models with the full quadrupolar interactions and the (approximate) isotropic interactions, we find discrepancies in the critical region to be typically (such as in the case of carbon dioxide) of the order of 4%. However, when the Lennard-Jones parameters are rescaled such that critical temperatures and critical densities of both models coincide with the experimental results, almost perfect agreement between the above-mentioned properties of both models is obtained. This result justifies the use of isotropic quadrupolar potentials. We also present a detailed comparison of our simulations with a combined integral equation-density functional approach and show that the latter provides an accurate description except for the vicinity of the critical point.
Collapse
Affiliation(s)
- B M Mognetti
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudinger Weg 7, D-55099 Mainz
| | | | | | | | | | | |
Collapse
|
42
|
Mognetti BM, Yelash L, Virnau P, Paul W, Binder K, Müller M, MacDowell LG. Efficient prediction of thermodynamic properties of quadrupolar fluids from simulation of a coarse-grained model: The case of carbon dioxide. J Chem Phys 2008; 128:104501. [DOI: 10.1063/1.2837291] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
|
43
|
Abstract
BACKGROUND Tecastemizole, a major metabolite of astemizole, is a potent and selective H1 receptor antagonist. Evidence suggests that this and certain other H1 receptor antagonists may possess anti-inflammatory effects that are, in some cases, independent of H1 receptor antagonism. Objective The aim of this study was to investigate the anti-inflammatory effects of tectastemizole in models of allergic inflammation. METHODS Effects of tecastemizole were assessed in a murine model of allergic lung inflammation, in passive cutaneous anaphylaxis (PCA) responses in guinea-pig skin and in in vitro assays measuring endothelial adhesion molecule expression and leucocyte-endothelial adhesion. RESULTS Tecastemizole inhibited antigen-induced eosinophil recruitment to the lungs of allergic mice in a dose-dependent manner. Furthermore, combination of a sub-effective dose of tecastemizole, combined with a sub-effective dose of dexamethasone inhibited eosinophil accumulation in this model. Plasma extravasation in PCA reactions was inhibited by tecastemizole, although by a mechanism that would appear to be H1 receptor-dependent. Cytokine-induced endothelial intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression, as well as mononuclear cell adhesion to human umbilical vein endothelial cells was inhibited by tecastemazole in a manner independent of H1 receptor antagonism. CONCLUSION These data suggest that tecastemizole may have H1 receptor-independent effects in inhibiting late-phase inflammatory responses, while acute responses appear to be inhibited in a H1 receptor-dependent manner. Furthermore, our data suggest an important potential steroid-sparing role for such drugs in the treatment of allergic inflammatory conditions.
Collapse
Affiliation(s)
- R Lever
- Department of Pharmacology, The School of Pharmacy, 29-39 Brunswick Square, London, UK
| | | | | | | | | |
Collapse
|
44
|
Vallée RAL, Paul W, Binder K. Single molecule probing of the glass transition phenomenon: Simulations of several types of probes. J Chem Phys 2007; 127:154903. [DOI: 10.1063/1.2794334] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
45
|
Ivanov VA, An EA, Spirin LA, Stukan MR, Müller M, Paul W, Binder K. Equation of state for macromolecules of variable flexibility in good solvents: a comparison of techniques for Monte Carlo simulations of lattice models. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 76:026702. [PMID: 17930169 DOI: 10.1103/physreve.76.026702] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2007] [Indexed: 05/25/2023]
Abstract
The osmotic equation of state for the athermal bond fluctuation model on the simple cubic lattice is obtained from extensive Monte Carlo simulations. For short macromolecules (chain length N=20 ) we study the influence of various choices for the chain stiffness on the equation of state. Three techniques are applied and compared in order to critically assess their efficiency and accuracy: the "repulsive wall" method, the thermodynamic integration method (which rests on the feasibility of simulations in the grand canonical ensemble), and the recently advocated sedimentation equilibrium method, which records the density profile in an external (e.g., gravitationlike) field and infers, via a local density approximation, the equation of state from the hydrostatic equilibrium condition. We confirm the conclusion that the latter technique is far more efficient than the repulsive wall method, but we find that the thermodynamic integration method is similarly efficient as the sedimentation equilibrium method. For very stiff chains the onset of nematic order enforces the formation of an isotropic-nematic interface in the sedimentation equilibrium method leading to strong rounding effects and deviations from the true equation of state in the transition regime.
Collapse
Affiliation(s)
- V A Ivanov
- Faculty of Physics, Moscow State University, Moscow 119992, Russia
| | | | | | | | | | | | | |
Collapse
|
46
|
Paul W, Strauch T, Rampf F, Binder K. Unexpectedly normal phase behavior of single homopolymer chains. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 75:060801. [PMID: 17677212 DOI: 10.1103/physreve.75.060801] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Indexed: 05/16/2023]
Abstract
Employing Monte Carlo simulations, we show that the topology of the phase diagram of a single flexible homopolymer chain changes in dependence on the range of an attractive square well interaction between the monomers. For a range of attraction larger than a critical value, the equilibrium phase diagram of the single polymer chain and the corresponding polymer solution phase diagram exhibit vapor (swollen coil, dilute solution), liquid (collapsed globule, dense solution), and solid phases. Otherwise, the liquid-vapor transition vanishes from the equilibrium phase diagram for both the single chain and the polymer solution. This change in topology of the phase diagram resembles the behavior known for colloidal dispersions. The interplay of enthalpy and conformational entropy in the polymer case thus can lead to the same topology of phase diagrams as the interplay of enthalpy and translational entropy in simple liquids.
Collapse
Affiliation(s)
- W Paul
- Institut für Physik, Johannes-Gutenberg-Universität, Staudingerweg 7, D-55099 Mainz, Germany
| | | | | | | |
Collapse
|
47
|
Martemyanova JA, Stukan MR, Ivanov VA, Müller M, Paul W, Binder K. Dense orientationally ordered states of a single semiflexible macromolecule: an expanded ensemble Monte Carlo simulation. J Chem Phys 2007; 122:174907. [PMID: 15910069 DOI: 10.1063/1.1888525] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Using a coarse-grained model we perform a Monte Carlo simulation of the state behavior of an individual semiflexible macromolecule. Chains consisting of N = 256 and 512 monomer units have been investigated. A recently proposed enhanced sampling Monte Carlo technique for the bond fluctuation model in an expanded ensemble in four-dimensional coordinate space was applied. The algorithm allows one to accelerate the sampling of statistically independent three-dimensional conformations in a dense globular state. We found that the temperature of the intraglobular liquid-solid transition decreases with increasing chain stiffness. We have investigated the possible intraglobular orientationally ordered (i.e., liquid-crystalline) structures and obtained a diagram of states for chains consisting of N = 256 monomer units. This diagram contains regions of stability of coil, two spherical globules (liquid and solid), and rod-like globule conformations. Transitions between the globular states are rounded first-order ones since the states of liquid, solid, and cylinder-like globules do have different internal symmetry.
Collapse
|
48
|
Affiliation(s)
- D. A. Anderson
- a Division of Applied Sciences , Harvard University , Cambridge , Massachusetts , 02138 , U.S.A
- b R.S.R.E. , Malvern , Wores , U.K
| | - W. Paul
- a Division of Applied Sciences , Harvard University , Cambridge , Massachusetts , 02138 , U.S.A
| |
Collapse
|
49
|
Vallée RAL, Van der Auweraer M, Paul W, Binder K. Fluorescence lifetime of a single molecule as an observable of meta-basin dynamics in fluids near the glass transition. Phys Rev Lett 2006; 97:217801. [PMID: 17155773 DOI: 10.1103/physrevlett.97.217801] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Indexed: 05/12/2023]
Abstract
Using single molecule spectroscopy, we show that the fluorescence lifetime trajectories of single probe molecules embedded in a glass-forming polymer melt exhibit strong fluctuations of a hopping character. Using molecular dynamics simulations targeted to explain these experimental observations, we show that the lifetime fluctuations correlate strongly with the average square displacement function of the matrix particles. The latter observable is a direct probe of the meta-basin transitions in the potential energy landscape of glass-forming liquids. We thus show here that single molecule experiments can provide detailed microscopic information on system properties that hitherto have been accessible via computer simulations only.
Collapse
Affiliation(s)
- R A L Vallée
- Department of Chemistry and Institute of Nanoscale Physics and Chemistry (INPAC), Katholieke Universiteit Leuven, Heverlee, Belgium.
| | | | | | | |
Collapse
|
50
|
Paul W, Queen LR, Page CP, Ferro A. Increased platelet aggregation in vivo in the Zucker Diabetic Fatty rat: differences from the streptozotocin diabetic rat. Br J Pharmacol 2006; 150:105-11. [PMID: 17099716 PMCID: PMC2013856 DOI: 10.1038/sj.bjp.0706957] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE Diabetes mellitus, especially type 2, is associated with increased arterial thrombosis. Our aims were (i) to characterize and compare platelet aggregation in vivo and in vitro in a type 2 diabetes model; and (ii) to determine whether these results differ from those in a type 1 diabetes model. EXPERIMENTAL APPROACH Platelet aggregation to ADP in lean or obese Zucker Diabetic Fatty (ZDF) rats and in streptozotocin (STZ)-treated or control Wistar rats was measured in vitro, using Born aggregometry, and in vivo, by (111)Indium-labelled pulmonary platelet accumulation. KEY RESULTS In vivo, ADP responses were higher in obese (type 2 model) than lean ZDF rats. However, in vitro, ADP aggregation did not differ between platelet-rich plasma from ZDF lean or obese rats; nor was any difference seen in ADP responses when platelets from either lean or obese ZDF rats were suspended in plasma from obese or lean ZDF rats, respectively. In vivo, ADP responses were similar in STZ treated (type 1 model) and control rats whereas, in vitro, isolated platelets from STZ diabetic rats were more responsive to ADP aggregation than controls. Platelets from control or STZ-treated rats suspended in plasma from STZ-treated rats exhibited reduced ADP aggregation, compared to when suspended in plasma from control rats. CONCLUSIONS AND IMPLICATIONS The platelet aggregation results obtained in vitro do not reflect those in vivo, therefore in vitro aggregation data should be interpreted with caution. Moreover, both in vitro and in vivo, different diabetic models exhibit important differences in platelet responsiveness.
Collapse
Affiliation(s)
- W Paul
- Sackler Institute of Pulmonary Pharmacology, School of Biomedical and Health Sciences, King's College London, London, UK
| | | | | | | |
Collapse
|